Certance DAT 72 Product manual
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DAT 72 and DDS-4 Tape Drives
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CD72LWH
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CD72LWE
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STD1401LW
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STD2401LW
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STD6401LW
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Product Manual
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Copyright © 2003 by Certance LLC. All Rights Reserved..
Part Number: 50000712, June 2003
Certance and the Certance logo are trademarks of Certance LLC. Seagate is a trademark of
Seagate Technology LLC. Other product names are trademarks or registered trademarks of their
respective owners.
Certance reserves the right to change, without notice, product offerings or specifications. No part
of this publication may be reproduced in any form without written permission from Certance LLC.
Certance provides this manual “as is,” without warranty of any kind, either expressed or implied,
including, but not limited to, the implied warranties of merchantability and fitness for a particular
purpose. Certance reserves the right to change, without notification, the specifications contained
in this manual.
Certance assumes no responsibility for the accuracy, completeness, sufficiency, or usefulness of
this manual, nor for any problem that might arise from the use of the information in this manual.
FCC Notice
This equipment generates and uses radio frequency energy and, if not installed and
used properly—that is, in strict accordance with the manufacturer’s instructions—
may cause interference to radio communications or radio and television reception. It
has been tested and found to comply with the limits for a Class B computing device
in accordance with the specifications in Part 15 of FCC Rules, which are designed to
provide reasonable protection against such interference in a residential installation.
However, there is no guarantee that interference will not occur in a particular
installation. If this equipment does cause interference to radio or television reception,
which can be determined by turning the equipment on and off, you are encouraged
to try to correct the interference by one or more of the following measures:
•
Reorient the receiving antenna.
•
Relocate the computer with respect to the receiver.
•
Move the computer into a different outlet so that the computer and receiver are
on different branch circuits.
If necessary, you should consult the dealer or an experienced radio/television
technician for additional suggestions. You may find the booklet, How to Identify and
Resolve Radio-TV Interference Problems, prepared by the Federal Communications
Commission, helpful. This booklet (Stock No. 004-000-00345-4) is available from the
U.S. Government Printing Office, Washington, DC 20402.
Warning.
Changes or modifications made to this equipment which have not been
expressly approved by Seagate may cause radio and television
interference problems that could void the user’s authority to operate the
equipment.
Further, this equipment complies with the limits for a Class B digital apparatus in
accordance with Canadian Radio Interference Regulations.
Cet appareil numérique de la classe B est conforme au Règlement sur brouillage
radioélectrique, C. R. C., ch. 1374.
The external device drive described in this manual requires shielded interface cables
to comply with FCC emission limits.
Additional Warnings:
•
To prevent fire or electrical shock hazard, do not expose the unit to rain or
moisture.
•
To avoid electrical shock, do not open the cabinet.
•
Refer servicing to qualified personnel.
About This Manual
This is the product manual for DAT 72 and DDS-4 internal and external tape drives.
It describes how to use the DAT 72 and DDS-4 drives.
Following are brief descriptions of the sections in this manual.
Chapter 1, “Introduction” provides general specifications, features and an
overview on DDS technology.
Chapter 2, “Specifications” contains physical, performance, environmental,
reliability, and power specifications.
Chapter 3, “Installation” provides cautions, unpacking tips, inspection information
and installation/connection steps.
Chapter 4, “Drive Operation and Maintenance” explains the operation of the drive
and describes necessary maintenance procedures.
Chapter 5, “Theory of Operations” details the functional operation of various
assemblies of the drive.
Chapter 6, “Data Compression” describes the data compression algorithm and
explains pertinent information for effective use of data compression.
iii
Contents
Contents
Introduction
1
Overview...................................................................................................................... 1
DDS Format Standard Compatibility ..................................................................... 1
DAT 72 and DDS-4 Capacity and Transfer Rates ................................................ 2
Features ...................................................................................................................... 3
DAT 72 and DDS-4 Drive Models................................................................................ 4
Specifications
7
Overview...................................................................................................................... 7
Physical Specifications ................................................................................................ 7
Power Specifications ................................................................................................... 9
Drive Performance Specifications ............................................................................. 10
Environmental Requirements .................................................................................... 12
Reliability ................................................................................................................... 12
Mean Time Between Failures ............................................................................. 13
Mean Time to Repair........................................................................................... 13
DDS Cartridge Specifications .................................................................................... 13
Regulatory Compliance ............................................................................................. 14
Installation
15
Introduction ................................................................................................................ 15
Unpacking and Inspection ......................................................................................... 15
Installing an Internal Drive ......................................................................................... 15
Guidelines and Cautions ..................................................................................... 16
Configuring an Internal Drive .............................................................................. 16
DIP Switch Settings............................................................................................. 18
Mounting an Internal Drive .................................................................................. 20
Installing an External Drive ........................................................................................ 24
Configuring the External Drive ............................................................................ 24
Connecting the SCSI Interface Cable ................................................................. 25
Connecting the Power Cord ................................................................................ 25
Drive Operation and Maintenance
27
Loading a Cartridge ................................................................................................... 27
iv
DAT 72/DDS Product Manual
Unloading a Cartridge ................................................................................................27
Initializing a Blank Cartridge ......................................................................................28
DDS Cartridge Compatibility ......................................................................................28
Write-Protecting a Cartridge ......................................................................................28
LED Codes.................................................................................................................29
Clean LED ...........................................................................................................30
Media LED...........................................................................................................30
Drive LED ............................................................................................................30
LED Code Summary ...........................................................................................31
Cleaning the Tape Heads ..........................................................................................31
When to Clean the Tape Heads ..........................................................................31
How to Clean the Tape Heads ............................................................................32
Automatic Drive Spin-Down and Write.......................................................................32
Operating the Drive in High-Temperature or Humidity Conditions ............................32
Data Compression .....................................................................................................33
Loading Revised Firmware from Seagate Firmware Cartridges................................33
Flash Memory......................................................................................................33
Firmware Download Process via Tape ...............................................................33
Theory of Operations
35
Overview....................................................................................................................35
Drive Mechanism.................................................................................................35
Motors and Control Circuits .......................................................................................38
Timing Tracking Circuitry.....................................................................................38
Signal-Processing Electronics.............................................................................38
Flash Memory ............................................................................................................38
Sensors......................................................................................................................39
Read-After-Write ........................................................................................................39
Media Recognition System (MRS).............................................................................40
About the DDS Data Cartridge...................................................................................40
Data Compression
43
Introduction ................................................................................................................43
Overview .............................................................................................................43
Data Compression Considerations......................................................................44
Hardware Compression.......................................................................................45
Data Integrity .......................................................................................................45
DCLZ Algorithm .........................................................................................................46
Simplified Compression Operation......................................................................46
Dictionary ............................................................................................................47
v
Contents
Simplified Decompression Operation.................................................................. 48
vi
DAT 72/DDS Product Manual
Figures
Figure 1. 3.5-Inch Internal Drive ........................................................................................................................4
Figure 2. Internal Drive with Drive Rails for Mounting in a 5.25-inch Drive Bay ................................................4
Figure 3. External Drive .....................................................................................................................................5
Figure 4. Internal Drive—Dimensions ................................................................................................................8
Figure 5. Internal DDS Drive with Rails—Dimensions .......................................................................................8
Figure 6. Jumper Settings for an Internal Drive ...............................................................................................17
Figure 7. DIP Switch Settings for an Internal Drive..........................................................................................18
Figure 8. Mounting an Internal Drive................................................................................................................20
Figure 9. Mounting Holes for an Internal Drive in a 3.5-inch Configuration (without mounting brackets) .......20
Figure 10. Mounting Holes for an Internal Drive in a 5.25-inch Configuration (with mounting brackets) ........21
Figure 11. Interface Connector on an Internal Drive........................................................................................22
Figure 12. Two SCSI Termination Examples for Internal Drives .....................................................................22
Figure 13. Power Connector on the internal Drives .........................................................................................23
Figure 14. Rear Panel of External Drives ........................................................................................................24
Figure 15. SCSI Termination Examples for External Drives ............................................................................25
Figure 16. Loading a Tape Cartridge ...............................................................................................................27
Figure 17. Location of the Eject Button and LEDs on internal Drives (external drive is similar) ......................28
Figure 18. Write-Protect Tab on a DDS Cartridge ...........................................................................................29
Figure 19. Front Panel of an Internal Drive (external drive is similar)..............................................................29
Figure 20. Four-Head Cylinder Design ............................................................................................................37
Figure 21. Alternating Azimuth Angles on Tape Tracks...................................................................................37
Figure 22. DDS Drive Cartridge Design Features............................................................................................41
Figure 23. Write-Protect Tab on the DDS Cartridge ........................................................................................41
1
Introduction
1
Introduction
Overview
The Seagate® DDS-4 (digital data storage) and DAT 72 (digital audio tape) drives are
designed for computer environments that require high-performance, high-capacity
data storage. Based on a 3.5-inch mechanism, the internal and external models
provide the following data storage capacities and native transfer rates:
DDS-4
DAT 72
Data Storage Capacity:
20 Gbytes
(40 Gbytes compressed)
36 Gbytes
(72 Gbytes compressed)
Native Transfer Rate:
2.75 Mbytes per second
(5.5 Mbytes per second
compressed)
3.5 Mbytes per second
(7.0 Mbytes per second
compressed)
The DAT 72 and DDS-4 drives combine established DAT technology, high-density
recording and hardware data-compression capability along with Seagate’s proven
computer-grade design to provide unmatched reliability and performance
characteristics among DDS products. The DAT 72 and DDS-4 drives are ideal for
workstation, server, and network/enterprise applications such as:
•
Backup of high-capacity fixed discs
•
Data interchange between systems
•
Network servers
•
Loader products
•
Online data collection
•
Near-line secondary storage for text, graphics or multimedia information of all
types
•
Archival storage
DDS Format Standard Compatibility
The DDS drive supports the DDS-4, DDS-3, and DDS-2 recording formats. The DAT
th
72 drive supports the DDS 5 Generation, DDS-4, and DDS-3 recording formats.
Compatibility with each of these standards ensures complete write and read
interchange of recorded digital data between all compliant drive and media vendors.
2
DAT 72/DDS-4 Product Manual
The DAT 72 and DDS-4 drives support DDS data compression. Compression
doubles a drive’s uncompressed capacity. For example, a 20 GB uncompressed
drive will be 40 GB with compression.
The DDS-4 drive complies with the following guidelines and specifications:
•
The DDS-2 recording format standard, ANSI/ECMA-198, 3,81mm Wide Magnetic
Tape Cartridge for Information Interchange - Helical Scan Recording - DDS-2
Format using 120 m Length Tapes
•
The DDS-3 recording format standard, ANSI/ECMA-236, 3,81mm Wide Magnetic
Tape Cartridge for Information Interchange - Helical Scan Recording - DDS-3
Format using 125 m Length Tapes
•
The DDS-4 recording format specification from ECMA-288: 3,81 mm Wide
Magnetic Tape Cartridge for Information Interchange - Helical Scan Recording:
DDS-4 Format
The DAT 72 drive complies with the following guidelines and specifications:
•
The DDS-3 recording format standard, ANSI/ECMA-236, 3,81mm Wide Magnetic
Tape Cartridge for Information Interchange - Helical Scan Recording - DDS-3
Format using 125 m Length Tapes
•
The DDS-4 recording format specification from ECMA-288: 3,81 mm Wide
Magnetic Tape Cartridge for Information Interchange - Helical Scan Recording:
DDS-4 Format
•
The DDS 5th Generation recording format specification from the HP DAT 72
Format Standard A5969-3050-1:3,81 mm Wide Magnetic Tape Cartridge for
Information Interchange - Helical Scan Recording - DAT 72 Format Using 170 m
Length Tapes.
Note:
For the latest ECMA standards, see the ECMA web site at
http://www.ecma.ch
DAT 72 and DDS-4 Capacity and Transfer Rates
The DAT 72 and DDS-4 drives provide the following capacities and transfer rates,
depending on the recording mode and the tape length:
Recording Mode
DDS-2*
DDS-3
DDS-4
DDS 5th Generation
Tape length
120 meters
125 meters
150 meters
170 meters
Capacity
(native)
4.0 Gbytes
12.0
Gbytes
20.0 Gbytes
36.0 Gbytes
Capacity
(compressed)
8 Gbytes
24 Gbytes
40 Gbytes
72 Gbytes
Transfer rate
(native)
1.375
Mbytes/sec
2.75
Mbytes/sec
2.75
Mbytes/sec
3.54 Mbytes/sec
* Applies to the DDS-4 drive only.
3
Introduction
In data-compression mode, the Seagate DAT 72 and DDS-4 drives typically double
the storage capacity and transfer rate of the native uncompressed operation. Tape
capacity and the sustained data-transfer rate are dependent upon the characteristics
of the files being compressed, the application software used, and system parameters
such as the speed of the host and the operating system. The DAT 72 and DDS–4
drives also offer synchronous or asynchronous SCSI transfers with a high-speed
burst data-transfer rates.
The DAT 72 and DDS-4 drives provide superb reliability through three levels of errorcorrection code (ECC) and the four-head design, which provides for read-after-write
(RAW) error detection and correction. The DAT 72 and DDS-4 drives also include a
“flying” preamplifier for greater signal-to-noise ratio.
Features
The DAT 72 and DDS-4 drives represent Seagate’s commitment to reliable
engineering and durable tape drive products that implement leading-edge
technology. Key features of the drives include:
•
A platform based on state-of-the-art sealed drive mechanism and tape-handling
components for improved immunity to airborne contaminants and extended
media life
•
Three available form factors: 3.5-inch internal for installation in a 3.5-inch halfheight space; 3.5-inch drive with factory-installed 5.25-inch mounting rails and
bezel for installation in a 5.25-inch half-height space; and external subsystem
with built-in, auto-sensing, worldwide power supply
•
ANSI/ECMA compliance and capability to write and read DDS 5 Generation
(DAT 72 only) DDS-4, DDS-3, and DDS-2 (DDS-4 only) cartridges
•
Advanced onboard DDS-DC hardware using Data Compression Lempel-Ziv
(DCLZ) data-compression algorithm
•
High-speed transfer rates for fast backups
DDS-4:
– 2.75 Mbytes per second typical—uncompressed data
– 5.5 Kbytes per second typical—compressed data
DAT 72:
– 3.5 Mbytes per second typical—uncompressed data
– 7.0 Kbytes per second typical—compressed data
•
High-performance SCSI burst transfer rate of 10 Mbytes per second
asynchronous and 80 Mbytes per second synchronous
•
Flash memory to store setup parameters and enable field firmware upgrades
•
Four-head design with RAW error detection and rewrites
•
Three levels of ECC to ensure data integrity
•
Uncorrectable error rate of less than 1 in 1015 bits
•
LVD / Ultra Wide SCSI connection
•
Automatic power-on self-test
•
Support for TapeAlert™ Certified Solutions
th
4
DAT 72/DDS-4 Product Manual
DAT 72 and DDS-4 Drive Models
The DAT 72 and DDS-4 3.5-inch and 5.25-inch internal drives are tailored for easy
installation in today’s computers, and the full-featured embedded SCSI controller
facilitates easy integration into a variety of systems. DAT 72 and DDS-4 models
include:
•
A 3.5-inch, half-height drive that mounts internally (see Figure 1)
Figure 1. 3.5-Inch Internal Drive
•
A 5.25-inch, half-height drive that consists of a 3.5-inch drive with 5.25-inch
mounting rails and bezel that mounts internally in a 5.25-inch, half-height space
(see Figure 2)
Figure 2. Internal Drive with Drive Rails for Mounting in a 5.25-inch Drive Bay
•
A complete external subsystem that contains the 3.5-inch drive and built-in
worldwide power supply (see Figure 3)
5
Introduction
Figure 3. External Drive
6
DAT 72/DDS-4 Product Manual
7
Specifications
2
Specifications
Overview
This chapter includes technical specifications for the internal and external SCSI
drives. This information covers the following specifications and requirements:
•
Physical specifications
•
Power specifications
•
Drive performance specifications
•
Environmental requirements
•
Reliability
•
DDS cartridge specifications
•
Regulatory compliance
Physical Specifications
The physical specifications of the internal and external DAT 72 and DDS-4 models
are listed in the following table:
Specification
Internal
Internal with rails
External
Height
1.6 in/41.2 mm
1.6 in/41.2 mm
2.7 in/69 mm
Width
4.0 in/101.6 mm
5.74 in/146.0 mm
6.1 in/152.0 mm
Length
5.7 in/146.0 mm
6.9 in/175.0 mm
9.3 in/235.0 mm
Weight
1.4 lb/0.62 kg
1.8 lb/0.87 kg
4.1 lb/1.8 kg
Figures 4 and 5 on the following pages show the dimensions of the internal 3.5-inch
and 5.25-inch drives.
8
DAT 72/DDS-4 Product Manual
41.3 mm
(1.63 in)
101.6 mm
(4.00 in)
13.0 mm (0.51 in)
2 places
3.8 mm (0.15 in)
5.0 mm (0.196 in)
2 places
94.0 mm
(3.70 in)
M3.0 x 4 deep min.
(10 places)
90.0 mm
(3.54 in)
2 places
70.0 mm
(2.75 in)
60.0 mm
(2.36 in)
2 places
31.0 mm
(1.22 in)
21.0 mm (0.83 in)
2 places
41.2 mm
(1.62 in)
146.0 mm
(5.75 in)
M3.0 x 4 deep min.
(4 places)
6.0 mm
(0.24 in)
Side View
101.6 mm
(4.00 in)
Bottom View
Note: Tolerance for all dimensions is 0.25mm (0.01 in)
Figure 4. Internal Drive—Dimensions
41.3 mm
(1.63 in)
31.5 mm (1.24 in)
21.8 mm (0.86 in)
146 mm
(5.75 in)
9.9 mm (0.39 in)
16-M3
174.6 mm
(6.87 in)
79.4 mm
(3.13 in)
47.6 mm
(1.87 in)
41.2 mm
(1.62 in)
139.7 mm (5.50 in)
149.1 mm (5.87 in)
Side View
Note: Tolerance for all dimensions is 0.25mm (0.01 in)
Bottom View
Figure 5. Internal DDS Drive with Rails—Dimensions
9
Specifications
Power Specifications
The following table lists the power specifications for the internal DAT 72 and DDS-4
drives.
Specification
+12 VDC supply
+5 VDC supply
Voltage Tolerance
Operational Current
Standby Current
Surge (peak)
Ripple (peak-to-peak)
+ or – 10% operating
250 milliamps max
15 milliamps max
600 milliamps max
≤ 100 mV (peak to peak)
+ or – 7% operating
1.35 Amps max
1.2 Amps max
1.5 Amps max
≤ 100 mV (peak to peak)
Total power consumption for the DAT 72 is as follows:
Standby Power
6.5 watts max
Operating Power
8.7 watts typical, 10.0 watts max
Surge (start up)
20.0 watts max (instantaneous peak)
Note: When measured over a 20-msec period, the maximum surge power is 14.0
watts.
Total power consumption for the DDS-4 (including both the +5V and +12V power
supplies) is as follows:
Standby Power
6.0 watts max
Operating Power
9.0 watts typical, 10.0 watts max
Surge (start up)
14.0 watts max
Note: Surge power and current are measured over a 20-msec period.
The following table lists pin assignments of the power connector for the internal DDS.
Pin
Assignment
1
+12 VDC
2
+12 return
3
+5 return
4
+5 VDC
The external drives have a built-in power supply that senses the incoming voltage
and automatically adapts to voltages within the range of 100 to 240 volts, 50 to 60
Hz. The following table lists the power specifications of the power supply.
Specification
AC Input Current
AC Input Power
Note:
100 (Japan)
100 milliamps
10.0 watts
AC Input Voltage
120 (US)
240 (European)
85 milliamps
170 milliamps
10.0 watts
10.0 watts
The drive employs a power-sensing circuit that automatically detects a loss
of supply voltage from the host. Temporary loss of supply voltage, or voltage
spikes, might result in the drive electronics being reset to their initialized
state, but shall under no circumstances result in a loss of recorded data.
10
DAT 72/DDS-4 Product Manual
Drive Performance Specifications
The following table lists the specifications for the DAT 72 drive.
Specification
Value
Capacity
125 m MP++
150 m MP+++
170 m MP++++
Track density (DAT 72)
24.0 Gbytes
40.0 Gbytes
72.0 Gbytes
Read-after-write (RAW)
Reed Solomon ECC (C3 - 3 levels)
4704 tracks per inch (TPI)
Recording unrecoverable errors
<1 in 1015 data bits
Tape drive type
Computer-grade 4DD mechanism
Head configuration
2 read heads, 2 write heads
Recording format
DDS 5th Generation
Recording method
Helical scan
Cartridge
73.66 mm × 53.34 mm × 10.16 mm
Transfer rate (sustained)
7.700 Kbytes per sec (DC ON)
Synchronous transfer rate (burst)
80 Mbytes per sec max
Asynchronous transfer rate (burst)
10 Mbytes per sec max
Search speed (max)
200x normal (3260 mm per sec)
Average access time
125 m cartridge
150 m cartridge
170 m cartridge
Drum rotation speed
< 30 seconds
< 30 seconds
< 40 seconds
10,000 Revolutions per Minute (RPMs)
Tape speed
2 meters per second
Head-to-tape speed
15.75 mm/second
Error recovery
11
Specifications
The following table lists the specifications for the DDS-4 drive.
Specification
Capacity (with 2:1 compression)
90 m MP
120 m MP+
125 m MP++
150 m MP+++
Track density (DDS)
Error recovery
Value
4.0 Gbytes
8.0 Gbytes
24.0 Gbytes
40.0 Gbytes
147.34 tracks per mm
Recording unrecoverable errors
Read-after-write
Reed Solomon ECC (C3 - 3 levels)
< 1 in 1015 data bits
Tape drive type
Computer grade 4DD mechanism
Head configuration
2 read heads, 2 write heads
Recording format
DDS-4
Recording method
Helical scan (R-DAT)
Cartridge
73.66 mm × 53.34 mm × 10.16 mm
Transfer rate (sustained)
5.500 Kbytes per sec (DC ON)
Synchronous transfer rate (burst)
80 Mbytes per sec max
Asynchronous transfer rate (burst)
10 Mbytes per sec max
Search speed (max)
400x normal (3260 mm per sec)
Average access time
90 m cartridge
120 m cartridge
125 m cartridge
Drum rotation speed
<30 sec
<40 sec
<40 sec
10,000 RPM (all DDS modes)
Tape speed
20.375 mm per sec.
Head-to-tape speed
20.4 mm per sec.
12
DAT 72/DDS-4 Product Manual
Environmental Requirements
The following table lists the environmental specifications for DAT 72 and DDS-4
drives. The internal drive should meet these standards if mounted either vertically
(on its side) or horizontally (right side up).
Specification
Operational
Nonoperational
Temperature
+41o
–40o to +149oF2
(–40o to + 65oC)
Below condensation
Thermal gradient
Relative humidity
Maximum wet bulb temperature
Altitude
Vibration
Sweep Test
Acoustic level idling (A-wt sum)
Acoustic level operational
(A-wt sum)
Shock (1/2 sine wave)
+113oF1
to
(+5o to + 45oC)
2oC per minute
(no condensation)
20% to 80%
noncondensing1
82.4oF (28oC)
–100 to +4,575 meters
1.20 mm peak-to-peak
(5–17 HZ)
0.73 G peak (17 to 150 Hz)
0.50 G peak (150–500 Hz)
(sweep rate 8 decades per
hour)
47 dBA maximum
53 dBA maximum
10 Gs peak, 11 msec
1. Mechanism and media
0% to 90%
noncondensing2
No condensation
–300 to +15,200
meters (power off)
1.5 g (5 to 500 Hz)
—
—
—
0
0
100 Gs peak,
11 msec
2. Mechanism
Reliability
The DAT 72 and DDS-4 drives are designed for maximum reliability and data
integrity. The following table summarizes the reliability specifications.
Specification
Value
Nonrecoverable error rate
< 1 in 10 bits
Error recovery and control
Error-correction code techniques (C1, C2, & C3 ECC)
Read-after-write (RAW)
DDS: N-Group writing (DDS-2 mode only)
Error monitoring and reporting (error log)
Retry on read
Data randomizer
Track checksum
412,000 hr at 20% duty cycle
15
Mean time between failures
(MTBF)
Mean time to repair (MTTR)
Less than 0.5 hour
13
Specifications
Mean Time Between Failures
The mean time between failures (MTBF) is specified at 412,000 hours minimum.
This specification includes all power-on and operational time but excludes
maintenance periods. Operational time is assumed to be 20 percent of the power-on
time. Operational time is the time the tape is loaded on the cylinder (tape moving
and/or cylinder rotating).
Note:
The MTBF rating does not represent any particular drive, but is derived from
a large database of test samples. Actual rates may vary from unit to unit.
Mean Time to Repair
The mean time to repair (MTTR) is the average time required by a qualified service
technician to diagnose a defective drive and to install a replacement drive. The
MTTR for DAT products is less than 0.5 hour (30 minutes).
The Seagate DDS drives are field-replaceable units. If a problem occurs with a
subassembly or component in the drive, you should replace the entire unit. Return
the drive to the factory in its original packaging. Contact your distributor, dealer, your
computer system company or your Seagate sales representative to arrange the
return.
DDS Cartridge Specifications
DDS drives provide maximum data integrity and reliability when Seagate-qualified
DDS cartridges are used as the recording media. Seagate maintains an ongoing
program to qualify manufacturers of DDS cartridges.
The following cartridges are recommended:
•
DDS-2 data cartridge: model STDM8, 120-meter tape (for DDS only)
•
DDS-3 data cartridge: model STDM24, 125-meter tape (for DDS only; read-only
for DAT 72)
•
DDS-4 data cartridge: model STMD40, 150-meter tape
•
DAT 72 data cartridge: model CDM72, 170-meter tape
•
DDS cleaning cartridge: model STDMCL or CDMCL
Contact your Seagate sales representative for information on qualified DDS data and
cleaning cartridge manufacturers and models.
14
DAT 72/DDS-4 Product Manual
Regulatory Compliance
The DAT 72 and DDS-4 drives comply with the regulations listed in the following
table.
Agency
Regulation
CSA
C22.2, No. 950-M89
TUV-RHEINLAND
EN 60 950
UL
1950
FCC
Class A and Class B1
CE
CE compliance
1. Required compliance for external model; verification on file for internal models.
Use these drives only in equipment where the combination has been determined to
be suitable by an appropriate certification organization (for example, Underwriters
Laboratories Inc. or the Canadian Standards Association in North America). You
should also consider the following safety points:
•
Install the drive in an enclosure that limits the user’s access to live parts, gives
adequate system stability and provides the necessary grounding for the drive.
•
Provide the correct voltages (+5 VDC and +12 VDC) based on the regulation
applied—Extra Low Voltage (SEC) for UL and CSA and Safety Extra Low
Voltage for BSI and VDE (if applicable).
15
Installation
3
Installation
Introduction
This chapter explains how to install the DAT 72 and DDS-4 drives. Some of the
information relates to all models; other information is specifically aimed at either the
internal or external models. The following paragraphs briefly outline the organization
of this chapter.
•
Unpacking and Inspection: contains general information that you should read
before installation.
•
Installing an Internal Drive: describes how to install a 3.5-inch internal drive
and a 3.5-inch drive with 5.25-inch mounting rails and bezel.
•
Installing an External Drive: describes how to install the external drive.
Unpacking and Inspection
Although drives are inspected and carefully packaged at the factory, damage may
occur during shipping. Follow these steps while unpacking the drive:
1.
Visually inspect the shipping containers and notify your carrier immediately of
any damage.
2.
Place shipping containers on a flat, clean, stable surface; then carefully remove
and verify the contents against the packing list.
If parts are missing or the equipment is damaged, notify your Seagate
representative.
3.
Always save the containers and packing materials for a future reshipment.
Installing an Internal Drive
Internal drive installation involves three main steps:
1.
Configuring the drive
2.
Mounting the drive
3.
Connecting the power and interface cables
16
DAT 72/DDS-4 Product Manual
Note:
Internal drives come in two mounting configurations for 3.5-inch and
5.25-inch drive bays, respectively. Drives configured for 5.25-inch bays are
identical to those used for 3.5-inch bays, except for the addition of drive
mounting brackets on each side of the drive and a different front bezel.
Installation procedures are the same for both drive configurations.
Guidelines and Cautions
The following guidelines and cautions apply to handling and installing the internal
drive. Keep them in mind as you install the drive.
•
Internal drives contain some exposed components that are sensitive to static
electricity. To reduce the possibility of damage from static discharge, the drives
are shipped in a protective antistatic bag.
•
Do not remove the drive from the antistatic bag until you are ready to install it.
•
Before you remove the drive from the antistatic bag, touch a metal or grounded
surface to discharge any static electricity buildup from your body.
•
Hold the drive by its edges only, and avoid direct contact with any exposed parts
of the printed circuit board (PCB).
•
Always lay the drive either on top of the antistatic bag or place it inside of the bag
to reduce the chance of damage from static discharge.
Configuring an Internal Drive
Before you install the tape drive in your computer, you may need to configure the
drive’s SCSI ID or other drive features. Jumpers located on the back of the drive
(between the SCSI interface and power connectors) are used to configure the SCSI
ID and to set parity checking and termination power. Other drive features are set
using a bank of DIP switches on the underside of the drive.
Default Settings
The default drive settings for the internal drive are listed below:
•
•
•
•
•
•
•
SCSI ID: 6
Media Recognition System (MRS) checking: enabled.
Parity checking: enabled.
Data compression: enabled.
Power-on self-test diagnostics: enabled.
Host operating system: Windows 98/Me/XP/NT/2000/2003 Server
SCSI interface compatibility: Wide SCSI supported (LVD and single ended).
If these default settings are appropriate for your needs, skip ahead to “Mounting an
Internal Drive” on page 20.
Jumper Settings
Configuration jumpers on the back of the drive are used to control the drive’s SCSI
ID, parity checking, and SCSI terminator power. The jumpers can also be used for
remote SCSI address selection. Figure 6 shows the locations of the jumper blocks
for the internal drive.
17
Installation
Default jumper settings shown
(SCSI ID 6, parity checking enabled,
and termination power disabled)
Pins:
1-2
3-4
5-6
7-8
9-10
11-12
Function:
SCSI ID bit 0
SCSI ID bit 1
SCSI ID bit 2
SCSI ID bit 3
Parity checking
Termination Power
SCSI ID=0
SCSI ID=8
SCSI ID=1
SCSI ID=9
SCSI ID=2
SCSI ID=10
SCSI ID=3
SCSI ID=11
SCSI ID=4
SCSI ID=12
SCSI ID=5
SCSI ID=13
SCSI ID=6
SCSI ID=14
SCSI ID=7
SCSI ID=15
Parity enable
Term. power
Figure 6. Jumper Settings for an Internal Drive
SCSI Address Selection (Pins 1 through 8)
You can select the SCSI address used by the drive by placing the appropriate
jumpers on pins pairs 1-2 through 7-8, as shown in Figure 6. The SCSI address
can also be selected remotely by connecting a SCSI address-selection switch to
pins 1 through 8.
Each SCSI device on a bus must have a unique SCSI ID. The SCSI controller or
host adapter generally uses ID 7. In some systems, the boot drive uses ID 0.
Note:
In an 8-bit SCSI mode, the drive only uses SCSI addresses 0 through 7.
Parity Checking (Pins 9 and 10)
If a jumper is installed on pins 9 and 10 (the default setting), parity checking is
enabled. If no jumper is installed, parity checking is disabled, but parity is still
generated by the drive.
18
DAT 72/DDS-4 Product Manual
Terminator Power (Pins 11 and 12)
Internal DAT 72 and DDS-4 drives are shipped with terminator power disabled (no
jumper across pins 11 and 12, as shown in Figure 6). You can enable terminator
power, if necessary, by placing a jumper across pins 11 and 12.
Note 1: If the termination power jumper is installed, be careful not to short the
TERMPWR signal to ground (for example, by attaching the SCSI cable
upside down). If this occurs, the drive no longer supplies terminator power to
the bus. The fuse resets automatically after the short is corrected.
Note 2: The internal DAT 72 and DDS-4 do not provide SCSI termination, and
therefore should not be installed as the last device in a SCSI chain. See
“Connecting the SCSI interface cable” for details.
DIP Switch Settings
Figure 7 shows the location of DIP switches on the underside of the internal drive.
Each of these switches is described in detail on the following pages.
If you change a DIP switch, the new setting does not take effect until you turn the
drive off, and then on again.
1
2
3*
4
5
6
7
8
9
10
O
N
Data compression (DC)
SCSI DC control
Media recognition
Self Test
Operating-system
configuration
switches
Wide/Narrow SCSI
Inquiry String support
Default settings shown
* Reserved on DAT 72
Front of drive
Figure 7. DIP Switch Settings for an Internal Drive
Data Compression (Switches 1 and 2)
If switch 1 is ON (the default setting), hardware data compression is enabled. If
switch 1 is OFF, hardware data compression is disabled.
If DIP switch 2 is ON (the default setting), SCSI commands can be used to enable or
disable hardware data compression. To prevent hardware data compression from
being enabled or disabled by SCSI commands, set DIP switch 2 to OFF.
19
Installation
Media-Recognition System (Switch 3)
The media-recognition system allows the drive to determine whether a given tape
cartridge conforms to the DDS tape standard. Use of non-DDS media may appear to
give satisfactory results, but the inferior specifications of such media can cause dataintegrity problems.
Switch 3 is reserved on DAT72 drives. On DDS-4 drives, switch 3 enables or
disables the media-recognition system (MRS). If switch 3 is ON (the default setting),
the drive reads and writes to MRS media and reads from but does not write to nonMRS media. If switch 3 is OFF, the drive reads or writes both MRS and non-MRS
media.
Power-on Self-Test Enable/Disable (Switch 4)
Switch 4 enables or disables execution of power-on self-test diagnostics when the
drive is powered on. If switch 4 is ON (the default setting), the drive responds to
SCSI commands only after successful completion of the self-test (about 5 seconds).
If switch 4 is OFF, the drive does not perform a power-on self-test.
Operating System Configuration (Switches 5 through 8)
Switches 5 through 8 configure the drive for use with UNIX and other non-Windows
operating systems. See the DAT 72 Configuration Guide or DDS-4 Installation
Manual for details. The default setting for all four of these switches is ON.
SCSI Wide/Narrow (Switch 9)
Switch 9 is reserved on DAT72 drives. On DDS-4 drives, switch 9 enables or
disables SCSI Wide operation on the SCSI bus. When switch 9 is ON (the default
setting), the drive is capable of operating in Wide (16-bit) SCSI mode. When switch 9
is OFF, the drive operates only as a Narrow (8-bit) SCSI device.
Note:
If switch 9 is set to OFF, the drive can use SCSI ID values 0 through 7 only.
Inquiry String Switch (Switch 10)
Switch 10 is used to select the Vendor ID that the drive returns when queried with a
SCSI Inquiry command. When switch 10 is ON (the default setting), the Vendor ID is
“SEAGATE DAT.” When switch 10 is OFF the Vendor ID is “ARCHIVE Python.” The
“ARCHIVE Python” Vendor ID may be used by independent software vendors to
provide software compatibility with previous Seagate DDS tape drives.
20
DAT 72/DDS-4 Product Manual
Mounting an Internal Drive
You can install your Seagate internal DDS drive
horizontally or vertically (on its side). Figure 8
shows a 3.5-inch drive being installed in a typical
system using side mounting screws.
Mounting the Drive in a 3.5-Inch Drive Bay
Mount the drive in a 3.5-inch drive bay and
secure it using two M3.0 metric screws on each
side of the drive. Do not use nonmetric screws or
screws longer than 4 mm or you might damage
the drive. As shown in Figure 9, the 3.5-inch
drive has four screw holes on the bottom and
five on each side.
Figure 8. Mounting an Internal Drive
41.3 mm
(1.63 in)
13.0 mm (0.51 in)
2 places
5.0 mm (0.196 in)
2 places
101.6 mm
(4.00 in)
3.8 mm (0.15 in)
94.0 mm
(3.70 in)
M3.0 x 4 deep min.
(10 places)
M3.0 x 4 deep min.
(4 places)
90.0 mm
(3.54 in)
2 places
70.0 mm
(2.75 in)
60.0 mm
(2.36 in)
2 places
31.0 mm
(1.22 in)
21.0 mm (0.83 in)
2 places
41.2 mm
(1.62 in)
146.0 mm
(5.75 in)
6.0 mm
(0.24 in)
Side View
101.6 mm
(4.00 in)
Bottom View
Note: Tolerance for all dimensions is 0.25mm (0.01 in)
Figure 9. Mounting Holes for an Internal Drive in a 3.5-inch Configuration
(without mounting brackets)
21
Installation
Mounting the Drive in a 5.25-Inch Drive Bay
If you are mounting the drive in a 5.25-inch drive bay, you must use a drive with
mounting brackets attached. As shown in Figure 10, the 5.25-inch drive brackets
have four screw holes on the bottom and six on each side.
41.3 mm
(1.63 in)
31.5 mm (1.24 in)
21.8 mm (0.86 in)
146 mm
(5.75 in)
9.9 mm (0.39 in)
16-M3
174.6 mm
(6.87 in)
79.4 mm
(3.13 in)
47.6 mm
(1.87 in)
41.2 mm
(1.62 in)
139.7 mm (5.50 in)
149.1 mm (5.87 in)
Side View
Note: Tolerance for all dimensions is 0.25mm (0.01 in)
Bottom View
Figure 10. Mounting Holes for an Internal Drive in a 5.25-inch Configuration
(with mounting brackets)
Connecting the SCSI Interface Cable
DAT 72 and DDS-4 drives can be used with two different types of SCSI interfaces:
Ultra2 SCSI (LVD) or “Wide” (16-bit) single-ended SCSI bus. The drive can
automatically detect whether it is connected to an LVD or single-ended wide SCSI
bus.
Note:
The DAT 72 and DDS-4 drives do not work in a SCSI-1 environment.
Connecting to a 68-pin Wide SCSI or LVD Bus
To connect the drive to an LVD or wide SCSI bus, first turn off all power to the drive
and computer. Then attach the interface cable to the SCSI interface connector on the
back of the drive (see Figure 11).
22
DAT 72/DDS-4 Product Manual
pin 34
Ultra2 SCSI 68-pin
high-density connector
pin 1
pin 35
pin 68
Figure 11. Interface Connector on an Internal Drive
SCSI Termination
The internal DAT 72 and DDS-4 drives do not provide SCSI termination. For this
reason, they should not be the last device on a SCSI chain. Two termination
examples are shown in Figure 12. If the drive is the only SCSI device, attach the
drive to the connector which is next to last on the SCSI chain and attach a multimode
terminator to the last connector in the chain.
SCSI Terminator
Tape drive
(no
)
termination
SCSI device
(termination
)
enabled
Tape drive
(no
)
termination
SCSI device
(termination
)
disabled
SCSI Controller
(termination enabled)
SCSI Controller
(termination enabled)
Figure 12. Two SCSI Termination Examples for Internal Drives
Connecting a Power Cable
Attach a four-pin power cable to the power connector on the back of the drive. Figure
13 shows the location of the power connector.
23
Installation
The recommended 4-pin power connector for the internal drive is an AMP 1-48024-0
housing with AMP 60617-1 pins or their equivalent.
Power connector
pin 4
+5V
pin 3: GND
(+5V return)
pin 1
12V
pin 2: GND
(+12V return)
Figure 13. Power Connector on the internal Drives
24
DAT 72/DDS-4 Product Manual
Installing an External Drive
The external drive is a compact external SCSI device that connects to the host
computer as a turnkey subsystem. Installing the external drive involves three simple
steps:
1.
Configuring the drive
2.
Connecting the SCSI interface cable
3.
Connecting the power cord
Configuring the External Drive
The following is the default configuration for the external drive:
•
The SCSI ID: 6
•
Media Recognition System (MRS) checking: enabled
•
Parity checking: enabled
•
Data compression: enabled
•
Power-on self-test diagnostics: enabled
•
Host operating system: Windows 98/Me/XP/NT/2000/2003 Server
•
Termination power: supplied to the SCSI bus
Note:
Some of these configuration settings can be changed using the SCSI Mode
Select command. SCSI command information for these drives is provided in
the product description manual.
Setting the SCSI ID
Make sure that the drive is turned off; and then set the SCSI ID for the drive using
the push-button switch on the back of the external drive. Figure 14 shows this switch,
as well as the two SCSI interface connectors, on/off switch, and the power-cord
connector.
Note:
The drive must be restarted, or a bus reset must occur for any change in a
SCSI ID to take effect.
68-pin wide SCSI
connectors
SCSI ID selector
On/Off Switch
+
–
Figure 14. Rear Panel of External Drives
AC Power
connector
25
Installation
Connecting the SCSI Interface Cable
The external drive provides two 68-pin, shielded connectors on the rear panel of the
enclosure. Either connector can be used as a SCSI IN or SCSI OUT connection (you
can use either connector to attach the drive to the host computer or to another SCSI
device).
Turn off your computer and all SCSI devices. Then attach a SCSI cable from the
host adapter or from another (unterminated) SCSI device to the external drive.
Note:
The DAT 72 and DDS-4 drives do not work in a SCSI-1 environment.
SCSI Termination
If the DAT 72 or DDS-4 drive is the last device or the only device in a SCSI chain,
you must install a terminating plug on the unused SCSI connector. See Figure 15 for
two SCSI termination examples.
External
SCSI device
SCSI Terminators
External
Tape Drive
External
Tape Drive
External
SCSI device
SCSI Controller
(termination disabled)
SCSI Controller
(termination enabled)
Internal
SCSI device
(termination
enabled
)
Example 1: SCSI termination Example 2: SCSI termination
in a system that has both
in a system that has only
internal and external SCSI
external SCSI devices.
devices.
Figure 15. SCSI Termination Examples for External Drives
Connecting the Power Cord
Attach the power cord securely to the power connector on the back of the drive. The
location of the power connector is shown in Figure 14.
26
DAT 72/DDS-4 Product Manual
27
Drive operation and maintenance
Drive Operation and Maintenance
4
Loading a Cartridge
Seagate DAT drives have a front-loading cartridge bay for easy operation. The drivebay door opens automatically when a cartridge is inserted. Figure 16 shows a
cartridge being inserted into a 3.5-inch internal drive. After you insert the cartridge,
there is a brief delay while the drive identifies the cartridge type and state and moves
the tape to the data area.
Figure 16. Loading a Tape Cartridge
Unloading a Cartridge
!
Caution. To ensure the integrity of your backups and restores, do not
push the eject button while the drive-status light-emitting diode (LED) is
ON. See Figure 17 for the location of drive LEDs.
Make sure that the amber drive-status LED is not lit. Then unload the cartridge by
pressing the eject button. For the location of the eject button, see Figure 17. After
you press the eject button, the drive automatically flushes the drive buffer to tape,
rewinds the cartridge, and updates the system log before ejecting the cartridge.
Up to three minutes may elapse between the time you press the eject button and the
time the cartridge is ejected. Do not power down the tape drive or the host computer
during this time.
28
DAT 72/DDS-4 Product Manual
Clean
LED
(green)
Media
LED
(green)
Drive
LED
(amber)
Eject
Button
Figure 17. Location of the Eject Button and LEDs on internal Drives
(external drive is similar)
Initializing a Blank Cartridge
When you insert a blank cartridge into the drive for the first time, the drive takes
about 10 to 12 seconds to determine that the tape is blank. The drive automatically
initializes the tape as soon as it receives a Write command from the host computer.
Initializing a blank tape takes about 30 seconds.
DDS Cartridge Compatibility
The Seagate DAT 72 and DDS-4 drives are designed to use data-grade DAT
cartridges, which comply with ANSI specifications listed in the “3.81 mm Helical-Scan
Digital Computer Tape Cartridge for Information Interchange,” ANSI X3B5/89-156
standard.
MRS cartridges have a series of alternate opaque and clear stripes at the beginning
of the tape. These stripes classify the media as datagrade.
Write-Protecting a Cartridge
Figure 18 shows how to write-protect or write-enable a DAT tape using the sliding
write-protect tab. You can only write data to the tape when the tab is in the writeenabled (closed) position.
29
Drive operation and maintenance
Write protected
Write enabled
Figure 18. Write-Protect Tab on a DDS Cartridge
LED Codes
As shown in Figure 19, the front panel of the DDS drive contains three LEDs that
provide information about both normal and error conditions. The external drive also
includes a green power-on LED on the front panel.
Clean
LED
(green)
Media
LED
(green)
Drive
LED
(amber)
Figure 19. Front Panel of an Internal Drive
(external drive is similar)
Eject
Button
30
DAT 72/DDS-4 Product Manual
Clean LED
If the Clean LED is ON continuously, the drive requires cleaning. Use only an
approved DDS cleaning cartridge. Following is a guideline for cleaning intervals
based upon drive type:
•
DDS-4
DDS2, DDS3, or DDS4 media has been operating in the drive for at least 50
hours.
•
DAT 72
DDS3, DDS4, or DAT 72 media has been operating in the drive for at least 50
hours.
If the Clean LED is flashing slowly (approximately ON 2 seconds, OFF 1 second),
the tape cartridge currently in use has exceeded a predefined soft-error threshold.
This signal is a warning only and does not indicate that data has been compromised.
If you see this signal, remove the tape at your earliest convenience and clean the
drive using an approved DDS cleaning cartridge. If, after cleaning the drive and
reinserting the original data cartridge, the Clean LED still flashes, you should use a
new cartridge for future backups.
If the Clean LED flashes rapidly, a cleaning cartridge that has exceeded its useful life
has been inserted into the drive. Replace the cleaning cartridge with a new approved
DDS cleaning cartridge.
Media LED
The Media LED functions as follows:
•
If the Media LED is ON (lit) continuously, a DDS cartridge has been inserted and
the drive is operating normally.
•
If the Media LED is flashing rapidly, the drive could not write to the tape correctly
(maximum rewrite count exceeded), and the write operation failed. Clean the
drive heads using an approved DDS cleaning cartridge. If you reinsert the
original data cartridge and the LED continues flashing, insert a new data
cartridge and retry the operation.
Note:
As routine maintenance, you should clean the drive heads after every 50
hours of operation.
Drive LED
•
If the Drive LED is ON continuously, the drive is reading from or writing to the
tape (that is, SCSI or tape movement is present). If you push the eject button
while the Drive LED is ON, you might lose data.
Note:
If your backup software issues a SCSI Prevent Media Removal command,
the Drive LED remains ON and the eject button is disabled so that the tape
cannot be accidentally ejected. To eject the tape, use you backup software’s
Eject function.
31
Drive operation and maintenance
•
If the Drive LED is flashing rapidly, a hardware fault has occurred. If this fault
occurs immediately after powering on the drive, then the Power-On Self-Test
switch is enabled and a Power-On Self-Test has failed. If the front panel LEDs
flash together, contact the Seagate Technical Support department for
information. If the Drive LED is flashing rapidly during drive operation, attempt to
remove the tape by pressing the eject button. If the tape does not eject within 2
minutes, press and hold the eject button continuously for more than 5 seconds.
The tape should eject within 40 seconds. Contact Seagate Technical Support for
more information.
LED Code Summary
The following table summarizes LED flash codes for the DAT 72 and DDS-4 drives.
LED
Action
Meaning
Clean
ON (lit)
Cleaning is required because the drive has been
operating for at least 50 hours.
Flashing
Slowly
Media
Drive
The internal error rate threshold has been
exceeded and cleaning is required.
Flashing
The cleaning cartridge in the drive has exceeded its
useful life. Replace the old cleaning cartridge with a
new one.
ON (lit)
A cartridge is inserted and is not generating
excessive errors.
Flashing
The drive could not write to the tape correctly (a
write error has occurred). Use a DDS cleaning
cartridge to clean the drive.
ON (lit)
The drive is reading from or writing to the tape
normally.
Flashing
Rapidly
A hardware fault occurred.
Cleaning the Tape Heads
When to Clean the Tape Heads
If excessive dust or debris from the tape media collects at one or more of the tape
heads, your drive might not be able to read from or write to the tape. To avoid this
situation, you must clean the tape heads on your DDS in the following
circumstances:
•
after every 50 hours of operation
•
if the Clean LED lights up or flashes
•
If the Media LED flashes during drive operation.
32
DAT 72/DDS-4 Product Manual
Note:
If cleaning the head does not correct a flashing LED condition, try using a
new data cartridge.
How to Clean the Tape Heads
To clean the tape heads on your drive, use only a Seagate-qualified DDS cleaning
cartridge. Seagate offers a cleaning cartridge, Model STDMCL or CDMCL, available
from http://shop.certance.com. Do not use an audio DAT cleaning cartridge. The
drive cannot recognize it.
After you insert the cleaning cartridge, the drive detects that the cartridge is a
cleaning cartridge, and loads and runs the cartridge for about 30 seconds. When
cleaning is complete, the drive ejects the cartridge.
Each time the cleaning cartridge is loaded, a new, unused portion of cleaning tape is
advanced over the entire tape path. The drive does not rewind a cleaning cartridge.
After about 30 cleaning cycles, the entire tape is used. If you insert a completely
used cleaning cartridge, the Clean LED flashes rapidly. Replace the cleaning
cartridge.
Automatic Drive Spin-Down and Write
To maximize tape and drive mechanism life, the drive automatically stops the
cylinder when no tape read or write activity occurs.
If a read or write operation occurs, normal operation resumes with no affect on the
host operation.
If tape write operations cease, a partially full data buffer may remain. After one
minute with no activity, the drive automatically writes the partial buffer to the tape.
This automatic action minimizes the possibility of lost data if the power fails.
If data to be written remains in the buffer when the eject button is pushed, the data is
written to tape before the tape is rewound and ejected.
Operating the Drive in High-Temperature or Humidity Conditions
Being faithful to the following guidelines can minimize the possibility of damaging the
drive due to operation during extreme temperature or humidity conditions (outside
the specified operating environment).
•
Use DDS cartridges only at temperatures between 5°C (40°F) and 40°C
(113°F). The cartridges can be stored at temperatures down to –40°C
(–40°F). Although the storage specifications range from 5°C to –40°C, do not
leave cartridges in severe temperature conditions—such as in a car in bright
sunlight. Avoid extreme changes in temperature or humidity whenever possible.
•
If cartridges are exposed to temperatures or humidities outside the specified
operating environment, condition the cartridges by exposure to the subsequent
operating environment for a time at least equal to the period the cartridges were
exposed to the out-of-spec environment.
Drive operation and maintenance
33
•
Place the drive in a position that provides stable temperatures. Do not place the
drive near open windows, fans, heaters or doors.
•
Do not read from or write to cartridges when a temperature change of 10°C per
hour is occurring.
Data Compression
Default operation for the DAT 72 and DDS-4 drives is to have data compression
enabled—the drive automatically compresses all data written to tape and
decompresses all compressed data read from tape.
The degree of compression varies with the type of data being processed.
Data with high degrees of redundancy, such as structured database files or graphics
files, can be compressed most efficiently, often at a ratio of 2:1 or more. Data with
little redundancy, such as executable programs, can be compressed the least.
The SCSI Mode Select command can switch the drive into compressed or
uncompressed mode for writing data regardless of the position of switch number 1
(see "Data compression (switches 1 and 2)" in Chapter 3). When reading, the drive
automatically selects compressed or uncompressed mode, depending on the data
that is read.
Loading Revised Firmware from Seagate Firmware Cartridges
Flash Memory
Another technological advancement incorporated into the DAT 72 and DDS-4 drives
is flash memory, which is useful if the drive’s SCSI firmware needs to be upgraded.
With the permanently installed, electrically upgradeable flash memory, revised SCSI
firmware for the drive can be loaded through:
1. Seagate OEM firmware cartridges
2. The host SCSI bus; or
3. The drive serial port.
The flash memory feature enables qualified OEMs who need to revise DAT 72 and
DDS-4 drive SCSI firmware to do so quickly and easily. Flash memory also prolongs
the life cycle of a drive because many new techniques—such as increasing the
capacity of the drive through support for longer tapes—may require only a firmware
upgrade.
Firmware Download Process via Tape
To load a firmware upgrade tape, follow these steps.
1.
Power on the host system with the DAT 72 or DDS-4 drive installed.
34
DAT 72/DDS-4 Product Manual
2.
Make sure that no applications are running that may try to communicate to the
drive during the firmware upgrade process. Close any such applications before
inserting the firmware upgrade cartridge.
3.
Insert the firmware upgrade cartridge.
!
Caution. Once the firmware upgrade cartridge is inserted into the drive,
it is important that no power interruption occurs while the firmware is
loading. Do not power off the drive. If a power interruption occurs, the
firmware may not be loaded correctly, and the drive may not operate
properly.
4.
The drive automatically recognizes the firmware upgrade cartridge and begins
downloading the firmware from the cartridge into DRAM.
5.
The drive ejects the firmware upgrade cartridge as soon as the firmware has
been completely downloaded into DRAM and the LEDs begin blinking with a
progressive pattern. When the blinking pattern stops, the firmware upgrade
operation is complete.
!
6.
Caution. Do not power down the host system or disconnect power to
the drive until you have completed step 6. Doing so could render the
drive inoperative.
Power down the system and reboot. The new firmware is immediately active
and operational.
Note:
At this time, it is recommended that you power cycle the drive to refresh any
new parameter information and to execute the power-on self-test to ensure
proper unit functionality.
Firmware upgrade cartridges are available only to qualified Seagate OEM
customers. Contact your Seagate sales representative for information.
Note:
The firmware can also be upgraded from a host computer via the SCSI
connection using software available at
http://support.certance.com/support/tape/utils/index.html.
35
Theory of operations
Theory of Operations
5
Overview
The Seagate DAT 72 and DDS-4 tape drive design integrates DAT technology
(helical scan recording method) into a true computer-grade data-storage peripheral
with industry-standard data-compression capability.
These drive designs are the result of:
•
Combining the economies of scale for key components, such as the cylinder,
heads, and audio Application Specific Integrated Circuits (ASICs), with a
computer grade drive (3.5-inch) using four direct drive motors and electronic
tape path control for the demanding computer storage environment.
•
Implementing a four-head design to provide read-after-write (RAW) error
correction and to maximize the benefits of the helical scan recording method,
namely: (1) high-density recording (all tape space is used by dense, overlapping
tracks at alternating azimuth angles) and (2) high-speed searches.
•
Using 5 -generation custom ASICs for efficient circuit layout and increased
reliability with low power consumption. These LSIs are quad-flat-pack (QFP)
designs that use complementary metal-oxide semiconductor (CMOS)
technology.
•
Using flash memory devices for easy firmware upgrades.
•
Storing configuration information in the parameter block of flash memory.
•
Implementing custom C3 ECC 1, 2, and 3 and other error-correction techniques.
•
Embedding a full-LSI SCSI controller with capability for SCSI-2 command sets in
LVD SCSI DDS-DC models.
•
Embedded 40 MHz (DDS-4) and 70 MHz (DAT 72) ARM CPUs with cache.
•
8-Mbyte SDRAM data buffer.
th
This chapter describes the DDS drive in more detail and explains implementationspecific information.
Drive Mechanism
The drive uses the helical scan recording method with a four-head cylinder design.
Four direct-drive motors and one brush-type motor are used in the drive. The read
and write functions use LSIs. Engineering decisions—such as the modular
partitioning of the electronics and use of surface-mount, low-power commercial and
custom LSIs—allow the drives to conform to the industry-accepted 3.5-inch form
36
DAT 72/DDS-4 Product Manual
factor. These design features are also important contributors to the overall reliability,
durability and performance of the drive.
The mechanism is designed for minimum tape wear and prevention of damage to the
tape. The modes or operational states, such as stop, rewind and play, reduce
mechanism and tape wear. Fewer mechanical mode changes result in less wear on
key drive components. In some cases, the need for a mode change is circumvented
using the Pause mode, which stops the tape without activating the mechanism. All
mode selection is performed by the controller firmware. The host computer does not
directly control mode selection.
A custom timing tracking design, combined with the four-head cylinder design,
implements the specifics of the DAT 72 and DDS-4 recording format standards and
provides the precision required to perform seamless appends, or the ability to add
subsequent recorded data frames immediately adjacent to the last data frames
written on the tape.
A bank of jumpers is available at the rear of the drive. These jumpers allow you to
set the SCSI ID for the drive and to change configuration choices. Refer to Chapter 3
for information about setting these jumpers.
By using the jumpers, you can also enable terminator power if needed. (The default
for internal models is with terminator power disabled. For external drives, the default
is with terminator power enabled.)
Note:
The DAT 72 and DDS-4 drives come with a terminator power fuse to provide
protection from component damage in case the SCSI cable is connected
incorrectly.
Three rectangular front-panel LEDs indicate a drive busy status and tape cartridge in
place status. When blinking, these LEDs also function as fault indicators. (Refer to
Chapter 4 for a summary of the function of these LEDs.) The external subsystem
also provides a round, green LED on the front panel to indicate that the power is on.
Helical Scan Recording—Four-Head Design
In helical scan recording, the heads are positioned opposite one another on a
cylinder, which is tilted approximately 6 degrees from the vertical plane and rotates
counterclockwise at 10,000 revolutions per minute (rpm). At the same time, the tape
moves slowly (20.375 mm per second in DDS-4 mode) in a horizontal path around
part of the cylinder. This simultaneous motion of cylinder and tape results in the head
traveling across the width of the tape in a helix-shaped motion.
The cylinder is designed with four, long-life heads—two read and two write heads.
These heads are set opposite one another with a rotation sequence of: write A, read
B, write B, read A (or write A new, read B old, write B new, read A old). The
advantage of this design is that a RAW check is performed immediately after the
data is written.
As mentioned earlier, the cylinder rotates rapidly (10,000 rpm) in the same direction
that the tape moves. The wrap angle of the tape on the cylinder is approximately 102
degrees. The combined movement of the tape and cylinder results in a relative headtape speed of 20.4 inches per second (ips).
37
Theory of operations
Figure 20 illustrates a helix track and the four-head design, and shows the
102-degree wrap angle.
6˚ Drum inclination angle
Direction of drum rotation:
Read Head B
Write Head B
Write Head A
Read Head A
Tape
Direction
Tape
Drum
102˚ Angle of tape wrap
Track of one
recording head
across tape surface
Figure 20. Four-Head Cylinder Design
The recorded tracks are written diagonally across the tape from bottom to top by
each write head. Because the head is wider than the track written, tracks overlap
with no tape space between them. In conventional recording, such overlap or even
proximity results in crosstalk (signals from adjacent tracks interfering with signals
from another track).
However, in helical scan recording, the heads are set at different azimuth angles so
that alternate tracks on the tape are written at alternate azimuth angles. (See Figure
21) Because the read head is set to the same angle as its corresponding write head,
it picks up a stronger signal from data written in the same azimuth angle as itself. So
it reads the track with minimal crosstalk. At the same time, the head is maintained
centered in the track by the timing tracking hardware and firmware.
Write head B
3 tape tracks
Write head A
20˚ head azimuth
Figure 21. Alternating Azimuth Angles on Tape Tracks
38
DAT 72/DDS-4 Product Manual
Motors and Control Circuits
The drive uses four direct-drive, brushless motors—the capstan, cylinder and two
reel motors. Using these small, direct-drive motors provides maximum reliability. The
cylinder motor rotates the cylinder. The capstan motor moves the tape. The mode
motor loads and ejects the cartridge. The two reel motors turn the tape reels.
The cylinder, capstan and reel servos are controlled by custom ASICs and the
motor-control firmware.
The fifth motor in the mechanism is a brush-type mode motor. This motor controls
(selects) the mechanism mode. Because the mode motor is not frequently used, and
due to space and torque requirements, a brush-type motor is best suited to this
application. The mode motor performs the mode changes as directed; for example,
this motor conditions the mechanism to eject the cartridge.
Timing Tracking Circuitry
The timing tracking circuitry of the drive is designed to provide high precision tracking
and head positioning. The timing tracking system, in conjunction with the four-head
read-after-write (RAW) design provides for reliable high-density data recording with
maximum storage efficiency.
Signal-Processing Electronics
The signal-processing electronics circuitry in the drive is made up of several
components. The drive’s main control microprocessor, data engine, and data buffer
management circuitry are all integrated in a single IC package. A single-chip DDS
formatter LSI communicates with the microprocessor and with the read and write
LSIs. The C3 ECC coprocessing capability and a second buffer memory control
function are also included in this IC. Other vital components are the highperformance SCSI LSI chip, the flash memory, and the DRAM buffer memory.
Flash Memory
Because the drive uses flash memory, the drive firmware can be easily upgraded
when new revisions of the firmware are released. The flash memory is 1 Mbyte in
size.
You can load new firmware in one of three ways:
Using a specially encoded firmware upgrade cartridge
Issuing a SCSI Write Data Buffer command to download the firmware to the
EEPROM
Through the drive serial port
39
Theory of operations
Refer to Chapter 4 for information about loading new firmware using a Seagate
firmware upgrade cartridge.
Sensors
A number of mechanical and optical sensors are integrated in the drive design. The
cartridge in and cartridge loading sensors are mechanical sensors that determine the
position of the loading mechanism. The other mechanical sensors report specific
information based on detecting the open or closed state of four recognition holes in
the DAT cartridge. The open or closed state of these holes designates tape type, that
is, whether the tape is a cleaning cartridge, whether the tape is prerecorded and
whether the tape cartridge is write-protected. These mechanical sensors and the
sensor for the cartridge in status comply with the DDS standard requirements for the
cartridge.
The beginning-of-tape (BOT) sensor is an optical sensor that uses the light path
transmissivity of leader tape, as specified in the DDS cartridge standards. The
sensor is also designed to recognize media recognition system (MRS) cartridges,
which have a series of alternate opaque and clear stripes at the beginning of the
tape.
The reel sensors for the two reels are optical. Optical sensors also detect the
mechanism position during mode changes.
The capstan sensor is a magnetoresistive Hall sensor that detects a magnetic field.
The cylinder sensors are coil and magnet sensors. Each reel motor contains a highresolution, optical-speed encoder.
Read-After-Write
The read-after-write (RAW) technique provides a means of verifying that host data
was written on the tape correctly by applying a read check immediately after writing
the data to tape. The read check is a comparison of the actual signal quality versus a
predetermined acceptable threshold level.
If a frame is identified as bad, it is rewritten later down the tape. The bad frame is not
necessarily rewritten immediately. It can be rewritten after three, four or five other
frames have been written. Any frame can be rewritten multiple times to provide for
skipping over bad areas on the tape.
Excessive consecutive rewrites typically signal a degraded media condition; in these
cases it is best to discontinue use of the tape in question and to continue with a new
tape.
During a read or restore operation, the threshold level is reduced to maximize the
likelihood that data can be successfully retrieved from tape. The combination of the
elevated read threshold during write operations, and of the reduced threshold during
read operations, ensures that data is written with the highest possible margin and
that recorded data can be read or retrieved with the highest possible confidence.
40
DAT 72/DDS-4 Product Manual
Media Recognition System (MRS)
The tape drive includes support for the media recognition system (MRS), which is
unique to DDS products.
The MRS refers to a series of alternate opaque and clear stripes at the beginning of
each tape. These stripes are used to classify the media as data- or computer-grade,
rather than audio-grade, media.
Internal to the drive is a system of optical sensors and electronics to identify the MRS
stripes to determine whether the tape is computer-grade media. The MRS capability
can be enabled or disabled using the drive’s DIP switch. When enabled, the drive
does not allow any write operations to any non-MRS tape cartridges.
All DDS-4 (150 meter), DDS-3 (125 meter), DDS-2 (120 meter), and DAT 72 (170
meter) tape cartridges have MRS striping to signal that they are computer-grade
media.
All DDS tape cartridges with the MRS striping either have the MRS logo, the MRS
acronym or media recognition system printed on them to readily distinguish them
from audio-grade media.
Audio-grade media is not suitable for data or computer backup purposes. Seagate
DAT drives eject audio tapes.
About the Data Cartridge
The tape drive is designed to use data-grade DDS/DAT cartridges, which comply
with the specifications in the 3.81-mm Helical-Scan Digital Computer Tape Cartridge
for Information Interchange, ANSI X3B5/89-156 standard. Seagate recommends
Seagate-qualified, data-grade DDS/DAT cartridges to ensure optimal data integrity
and reliability.
Seagate also recommends the use of a Seagate-qualified DDS head-cleaning
cartridge (Model STDMCL or CDMCL).
Note:
Proper maintenance of the drive requires that you use the DDS headcleaning cartridge after every 50 hours of read/write operation and whenever
the rectangular, green cartridge-in-place LED flashes during operation.
You can order both data and head-cleaning cartridges from Seagate. They are
packaged in multiples of five.
These small (approximately 2 inches × 3 inches × 0.4 inch) cartridges house a
magnetic tape that is 3.81 mm (0.150 inch) wide. The DDS cartridges are slightly
bigger than a credit card. Figure 22 shows the key features of the DDS cartridge.
41
Theory of operations
File Protect Hole
(Restorable)
Datum Holes
(4)
Recognition
Holes (1, 2, 3, 4)
Slider Lock (1)
(3)
(2)
(1)
Lid Lock
(Locked by Slider)
Slider Lock (2)
Figure 22. DDS Drive Cartridge Design Features
Qualified DDS cartridges are designed with specific write-protect, lid and other
features for information interchange and are tested to comply with the ANSI DDS
specifications.
The DAT 72 and DDS-4 drives also recognize all MRS cartridges when MRS is
enabled. MRS cartridges have a series of alternate opaque and clear stripes at the
beginning of the tape. These stripes classify the media as data-grade, rather than
audio-grade media. Figure 23 shows the four recognition holes that allow the drive
sensors to identify the type of tape, its magnetic thickness, and whether the tape is
prerecorded, unrecorded or is a cleaning cartridge. Other cartridge features allow the
drive to determine the cartridge in, BOT and EOT points.
The cartridge also provides for write protection so that existing data on the cartridge
is not overwritten (See Figure 25). A write-protected cartridge allows the existing
data to be read but does not allow new data to be written to the tape.
Note:
A write-protected cartridge
prevents the system log (in
the system area) from being
updated.
Figure 23. Write-Protect Tab on the
DDS Cartridge
Write
Enabled
Write
Protected
42
DAT 72/DDS-4 Product Manual
43
Data compression
Data Compression
6
Introduction
Overview
Typical data streams of text, graphics, software code or other forms of data contain
repeated information of some sort, whether it is at the text level where you can
readily recognize regular repetitions of a single word or at the binary level where the
repetitions are in bits or bytes. Although most data is unique and random, the binary
level data exhibits patterns of various sizes that repeat with varying degrees of
regularity.
Storage efficiency is increased if the redundancies or repetitions in the data are
removed before the data is recorded to tape. Data compression technology functions
to significantly reduce or eliminate the redundancies in data before recording the
information to tape. The compression increases the amount of data that can be
stored on a finite medium and increases the overall storage efficiency of the system.
With data compression, the redundant information in a data stream is identified and
then represented by codewords or symbols, which allow the same data to be
recorded in a fewer number of bits. These symbols or codewords point back to the
original data string, using fewer characters to represent the strings. Because these
smaller symbols are substituted for the longer strings of data, more data can be
stored in the same physical space.
Some important benefits result from data compression in DAT drives:
•
The same amount of information can be stored on a smaller length of tape.
•
Increased data density on a given length of tape.
•
Performance can more closely parallel to that of high-transfer-rate computers.
•
More information can be transferred in the same time interval.
44
DAT 72/DDS-4 Product Manual
Data Compression Considerations
In an effective data-compression method, several factors are important:
•
The amount of compression (measured by the compression ratio, which is a ratio
that compares the amount of uncompressed data to the amount of compressed
data and is obtained by dividing the size of the uncompressed data by the size of
the compressed data)
•
The speed with which data is compressed and decompressed in relation to the
host transfer rate
•
The types of data to be compressed
•
The data integrity of the compressed data
The amount of compression possible in a data stream depends on factors such as
the data pattern, the compression algorithm, the pattern repetition length, the pattern
repetition frequency, the object size (block of information to be compressed) and the
starting pattern chosen.
The transfer rate depends on factors such as the compression ratio, the drive buffer
size, the host computer input/output (I/O) speed, the effective disc speeds of the host
computer and the record lengths that the host computer transmits.
Data compression algorithms can be tailored to provide maximum compression on
specific types of data. But because varying types of data are encountered in normal
day-to-day operating circumstances, an effective data compression method for a
tape drive must serve various data types. Additionally, the data compression method
must adapt to different data types, automatically providing optimum handling for all
types of data.
Considering these factors, Seagate engineers concluded:
The most effective data compression method must compress as much data as
possible while assuring that
•
The transfer rate of the host computer is not impeded.
•
Adaptation is made to different types of data.
•
Data integrity is maintained.
45
Data compression
Hardware Compression
If data compression is used in software on the host computer rather than in the
hardware of the drive, you can slow down the transfer rate of the host because it
must perform compression computations in addition to its regular computations.
Also, any other host that wants to retrieve (decompress) the data must have the
same software.
Hardware data compression (HDC) refers to the implementation of the DCLZ
algorithm in the data compression engine, with the compression processing activity
transparent to the host computer and the user.
Seagate’s data compression engine is designed to provide a complete data
compression system using the DCLZ algorithm. This IC provides support circuitry as
well as the core DCLZ compression machine.
A more detailed description of the data compression engine is given later in this
chapter.
Data Integrity
There are various types of data-compression algorithms, but in this document they
are divided into two basic types: lossless algorithms, such as DCLZ or ALDC, and
lossy algorithms, such as those used in some consumer audio products.
Lossy algorithms drop out or lose some portion of repetitious data during the
compression process to reduce the actual data bytes that are recorded to tape. The
data lost during this process is lost forever and cannot be recovered. In consumer
audio, this is not a problem because this method reduces required storage space
and still provides better-than-analog recording and playback quality.
As you would expect, lossy algorithms are inappropriate for computer data storage of
any type; hence the choice of lossless algorithms for computer data storage use.
Lossless algorithms are designed to compress data using a complex algorithm,
ensuring that all data is compressed and recorded to tape and that all data can be
decompressed and returned in the identical format as before. No bits are lost, and no
data is compromised.
The DDS standards specify the use of the DCLZ algorithm, a lossless algorithm for
data compression.
46
DAT 72/DDS-4 Product Manual
DCLZ Algorithm
Within the computer industry, algorithms developed by Abraham Lempel and Jacob
Ziv (enhanced later by Terry Welch) are popular, versatile and powerful compression
methods. These LZ algorithms are basically of two types—LZ1, a sliding window
method, and LZ2/LZW, a hashed directory method.
LZ2 and LZW (Lempel-Ziv-Welch) are algorithms based on the hashed dictionary
method; these algorithms offer an acceptable compromise between speed and
compression ratio. This type of algorithm builds a symbol dictionary to represent
strings as the data is processed and then looks up matching patterns in the
dictionary. By monitoring the compression ratio in this type of algorithm, a new
dictionary can be started when the ratio drops, indicating a change in the data type.
This type of algorithm is responsive to changing data patterns while maintaining
acceptable speed.
Although dependent on the particular implementation, the LZ2/LZW type of algorithm
is generally faster than the LZ1 type because the dictionary structure promotes
efficient searching.
The DCLZ algorithm used in the DDS tape drive is based on the LZ2/LZW algorithm
type described earlier in this chapter. This algorithm has been approved by the US
ANSI standards group and the European ECMA standards group. Both the DDS
Manufacturers Group and QIC tape industry-standards committees accept DCLZ as
an approved standard. Within the DDS Manufacturers Group, DCLZ is the only
approved standard, ensuring complete interchange across all DDS drives and media.
Simplified Compression Operation
The following steps describe a simplified version of operation of the algorithm for
compressing data:
1.
From the current position in the input data stream, the algorithm fetches bytes
(characters) until a string is formed that does not have a matching entry in the
dictionary.
2.
The codeword for the longest string that has an entry in the dictionary (all bytes
except the last) is output.
3.
A dictionary entry for the string formed in step 1 is created.
4.
The current position is moved to the last byte of that string.
5.
Steps 1 through 4 are repeated until the input data stream is completely
processed.
47
Data compression
The following table illustrates this simplified operation.
Input
Byte
R
I
—
N
—
T
—
I
—
N
T
—
I
N
—
Current
String
R
RI
I
IN
N
NT
T
TI
I
IN
INT
T
TI
TIN
N
Match
Y
N
Y
N
Y
N
Y
N
Y
Y
N
Y
Y
N
Y
Build
Entry
—
RI
—
IN
—
NT
—
TI
—
—
INT
—
—
TIN
—
Output Code
Value
—
(R)
—
(I)
—
(N)
—
(T)
—
—
(IN)
—
—
(TI)
—
Dictionary
The dictionary is built and contained logically in external RAM and is not output as a
distinct item. Rather, the decompressor recreates the dictionary to recreate the
original data.
The dictionary allows up to 4,096 entries with each entry made up of:
•
The unique string found in the data stream
•
The codeword for that string
Codewords represent strings of up to 128 characters and are formed by adding a
new character to an existing codeword. These codewords range from 9 through 12
bits in size and are assigned a number in the range 0 through 4,095.
These codewords are either control flags, encoded bytes or dictionary codes:
•
Control Flags, codewords 0 through 7: These control flags are reserved
codewords that flag specific conditions as follows:
0
1
2
3
4–7
•
Dictionary frozen
Dictionary reset
Increment codeword size
End of record (EOR)
Reserved
Encoded bytes, codewords 8 through 263: These encoded bytes represent
single bytes of the input data stream and contain the values 0 through 255.
48
DAT 72/DDS-4 Product Manual
•
Dictionary codes, codewords 264 through 4,095: The dictionary codes refer
to dictionary entries and represent multiple bytes (a string of characters) in the
input data stream. These codes are built as the input stream is processed.
These codes are pointers to other locations and eventually end by pointing to
one of the byte values 0 through 255. A linked chain is created that builds up a
string of characters.
Each dictionary entry is 23 bits long and comprises a logical RAM address. The
information is stored in 8-bit-wide static RAM chips that are 8K, 10K, or 16K by 22
bits. The structure of each dictionary entry is as follows:
•
Bits 0 through 7 contain the byte value of the entry.
•
Bits 8 through 19 contain the codeword that represents the entry or that points
to a previous entry (encoded byte or dictionary code).
•
Bits 20 through 22 are condition flag bits.
Dictionary codewords range from 9 through 12 bits in length and correspond to
dictionary entries from 0 through 4,095. These entries are divided as follows:
•
First 512 entries are 9-bit codewords.
•
Second 512 entries are 10-bit codewords.
•
Next 1,024 entries are 11-bit codewords.
•
Final 2,048 entries are 12-bit codewords.
Simplified Decompression Operation
The DCLZ algorithm requires that compression and decompression be tied together
through:
•
The compression and decompression processes (requires synchronization)
•
The packing and unpacking of codewords into a byte stream (requires
synchronization)
That is, decompression of the data does not begin at an arbitrary point; rather, it
begins at a point where the dictionary is reset—known to be empty. This stipulation
is vital because the dictionary is embedded in the codewords, which saves time and
space as it is not recorded separately.
Likewise, the packing and unpacking processes require synchronization so that the
compressed data is presented to the algorithm in the proper order.
49
Data compression
The following steps describe a simplified version of the operation of the algorithm for
decompressing data.
1.
From a reset dictionary point, (which contains only control codes and encoded
bytes) codewords are fetched from the input stream and looked up in the
dictionary.
2.
New dictionary codes are built by combining the previously received codewords.
(The dictionary created during compression is recreated, guaranteeing that any
codeword received is contained in the dictionary.)
Codewords that are encoded bytes are output directly. Codewords that are dictionary
codes lead the algorithm through a series of bytes and codewords that point to other
dictionary entries. Bytes are stacked until an encoded byte occurs; then, the stack is
output.
The following table illustrates the reverse process of compression, showing a
simplified decompression operation.
Input
Code
Value
Byte
Value
Pointer
Root?
LIFO
Entry
Output
Byte
(R)
(I)
(N)
(T)
(IN)
—
(TI)
—
—
(N)
R
I
N
T
N
I
I
T
—
N
—
—
—
—
(I)
—
(T)
—
—
—
Y
Y
Y
Y
N
Y
N
Y
—
Y
R
I
N
T
N
NI
I
IT
—
N
—
RI
IN
NT
—
TI
—
INT
—
TIN
R
I
N
T
—
I
—
T
I
N
The following table shows the dictionary based on the preceding table.
Codeword
(RI)
(IN)
(NT)
(TI)
(INT)
(TIN)
Byte Value
I
N
T
I
T
N
Code Value
(Pointer)
(R)
(I)
(N)
(T)
(IN)
(TI)
Publication Number: 50000712 Printed in USA
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