SAS and SATA Team Up for the Enterprise

SAS and SATA Team Up for the Enterprise
white paper
SAS and SATA Team Up
for the Enterprise
Executive Summary
The enterprise is currently experiencing unprecedented need
for storage while at the same time being constrained by flat
IT budgets.
Serial data transmission, which offers performance capable
of scaling with ever-growing enterprise storage needs, is
rapidly making inroads into disk drive interconnect technology,
promising to eventually replace existing parallel architectures.
Legacy parallel Advanced Technology Attachment (ATA) drives,
long a commodity desktop storage item, are being replaced by
serial ATA (SATA) drives, which raise the ceiling on performance
and do away with bulky cables while maintaining a commodity
pricing structure. Newer SATA drives that are specifically
designed with enterprise storage features offer improved
reliability that rivals traditional Fibre Channel (FC) and
Small Computer System Interface (SCSI) drives.
Complementing these advancements in SATA are the equally
impressive performance gains being made with Serial Attached
SCSI (SAS) drives. Small form-factor (2.5") SAS drives are being
offered with greater I/O throughput, reliability improvements,
and the ability to scale far beyond what was possible with
traditional parallel SCSI drives.
LSI Logic Corporation
Harry Mason
Director Industry Marketing
Storage Standard Products
A robust SAS infrastructure, which supports both the new SAS
and SATA drives without any bridging, enables new options for
delivering diverse storage solutions. For the first time in the
history of enterprise computing, IT managers are now able to
mix storage drives within the same infrastructure, targeting
Intel Corporation
Scott Peiffer
Product Line Manager
Storage Platforms
Storage Server Marketing
Western Digital Corporation
Hubbert Smith
Director
Enterprise Marketing
different types of storage to different application needs. This
provides an exceptional opportunity for OEMs and systems
integrators to leverage a common infrastructure in servicing
a broad range of customer needs.
SAS and SATA Team Up for the Enterprise
Enterprise Storage Expanding Rapidly
Enterprise Storage Solutions Today
A number of factors are pushing rapid growth in enterprise stor-
The storage industry provides three hard disk drive options
age and creating demand for technology companies to respond
with varying levels of cost and performance: They are Fibre
to many different customer needs. Demands for faster, cheaper,
Channel, SCSI/SAS and SATA (see Table 1).
better, and more storage fall into well-defined areas:
Each storage technology offers different advantages suited
• More storage capacity. Demand for enterprise storage is
to different usage models. Unfortunately, they are not inter-
coming from new areas such as rich media, Enterprise
changeable within an infrastructure without the use of
Resource Planning (ERP) applications, and growing regulatory
expensive bridging technology. This tends to lock enterprises
requirements, as well as an increasing emphasis on backup
into a particular technology and limit scalability.
and data recovery.
FC and SCSI systems offer high-performance options
• Low-cost storage. While the demand for capacity is increasing,
such as multi-host failover support that are inherently designed
IT budgets aren’t budging. Traditional Storage Area Network
for high-availability mission-critical applications. Both FC and
(SAN) infrastructures in many instances are too expensive to
SCSI use common command structures based on the 20-plus-
meet the growing demand and will need to be replaced by
year SCSI legacy of enterprise-proven middleware. These drives
new lower-cost alternatives that offer comparable reliability
are critical in environments where transactions-per-second
and performance.
is important and have a rugged construction that maintains
low-vibration characteristics under extreme workload environ-
• Scalable storage. More than ever, IT organizations are being
ments. Hundreds of these drives can work cooperatively in
tasked to develop an infrastructure that can flex and grow with
an infrastructure without impacting drive performance, data
the business. In many instances, IT managers must make hard
availability or data reliability. Moreover, the legacy middleware
tradeoffs as to whether they want a storage infrastructure that
applications that support these drives are enterprise-proven
can grow based on low cost or high performance.
and offer a low-risk approach to storage.
As enterprise data grows a variety of new storage applications
• Higher performance storage. New enterprise requirements
such as ERP, e-Commerce, data warehousing, and enterprise
arise, users demand lower cost alternatives, especially in situa-
grid computing require higher performance. There is also a
tions where data may be less frequently accessed. Applications
need to back up data without affecting performance.
that require infrequently accessed storage, such as archiving
Table 1: Enterprise Storage Solutions
Features
Fibre Channel
SCSI/SAS
SATA
SATA for enterprise
Performance (Speed)
2 Gbps (now)
4 Gbps (new)
8 Gbps (future)
Ultra320 (now)
3 Gbps (new)
6 Gbps (future)
1.5 Gbps (now)
3.0 Gbps (new)
3.0 Gbps (new)
10K -15K
10K - 15K
7.2K-10K
7.2K- 10K
Typical Large Capacity
146GB
146GB
400GB
400GB
Typical MTBF (Hour)
1.4 M
1.4 M
600K
1.2 M
$3.50 - $3.001
$3.40 - $2.601
$1.00 - $0.751
$1.00 - $0.801
Usage Rating
High duty cycle, server
and networked storage
High duty cycle, server
and networked storage
Form Factor
3.5 & 2.5
3.5 & 2.5
Performance (RPM)
$/GB
High duty cycle, server
and networked storage
3.5 & mobile SATA2
1. Prices are approximate for small quantity (<10K purchases), and may vary based upon performance, reliability and form factors.
2. Pricing for small form factor drives (2.5") including mobile SATA drives generally have a 40%+ $/GB premium.
2
3.5
SAS and SATA Team Up for the Enterprise
files, backing up systems, and referencing data, can benefit
data storage environment have increased. As a result, many
from lower cost storage technology.
enterprises are now finding that they need to migrate to serial
SATA drives incorporate improved reliability features over their
interface technology sooner rather than later in order to keep
parallel predecessors. New improvements, such as extended
up with the mounting business pressures that are demanding
disk drive platform reliability, error recovery, queuing, and jumper
more and more from their storage infrastructure.
elimination, have been responsible for SATA moving into the
enterprise world where it has found acceptance as Web server
Serial Choices
and Redundant Array of Inexpensive Disks (RAID) storage. Vendors
Fibre Channel drives have always been serial. Fibre Channel
have eliminated the bulky flat-ribbon cables and incorporated
systems operating at 4 Gbps are expected to begin shipping later
hot-swapping, a requirement of many enterprise environments,
this year, and the roadmap to 8 Gbps has been ratified by the
into the SATA plug. SATA drives support these application
Fibre Channel Industry Association (FCIA).
environments by increasing the performance ceiling established
by parallel ATA drives but retaining the commodity pricing
established by desktop volumes.
The Evolution to Serial Technology
Fibre Channel drives are typically found in external storage subsystems that have been connected to the host through a Fibre
Channel SAN. While based on the same standard, the interfaces
can take on different characteristics depending upon whether its
primary use is as a SAN-attach or drive-attach. The connections
Serial Data Transmission will Eventually
Replace Parallel.
to the host are primarily Host Bus Adapters (HBAs) that commu-
Engineering challenges with parallel transmission, including
subsystems. While the infrastructure can be costly in some
crosstalk, ground bounce, ringing, and clock skew, grow harder
instances, users are able to share data more freely and more
to overcome as data transmission speeds increase, to the point
efficiently between a large number of distributed hosts. Also, the
where parallel technology has reached its upper bound. As disk
dual-port nature of this interface provides a failover capability
drive platter speeds and data density increase, the interface
that other interfaces like SAS are just beginning to exploit.
between the drive electronics and the controller card must
SAS drives will be available in mid-2005. The emergence of
handle ever faster data transfers. The only way to meet this
2.5" SAS form factors enables new classes of high-performance,
demand is with serial data transmission.
highly available RAID systems in racks as small as a 1U. Faster
Serial disk drive technology is already pervasive as the inter-
interface rates for the drives and better scalability than parallel
connect technology for SAN and Network Attached Storage (NAS)
SCSI offers users the capability of incrementally expanding stor-
environments, where it is required to meet the need for distance
age capability. It also offers better investment protection than
and storage consolidation. However, this usage is only about
the parallel interfaces of today.
20 percent of the disk drive interconnects. Now the market is
Market data forecasts for 2006 predict that installation of SAS
discovering that point-to-point serial architectures are required
drives will surge and become a significant percentage of overall
to improve system reliability, reduce cabling congestion (where
SCSI shipments. SAS drives will find their way into traditional
cables are necessary), and to enable the infrastructure to scale
SCSI markets, primarily standard high-volume servers, as
with the insatiable demand for accessing more data quickly.
well as external storage enclosures that can be cascaded with
Parallel technologies comprise a large portion of the installed
the use of SAS expanders. Unlike Fibre Channel, the SAS infra-
storage base in today’s enterprise, and it’s likely to remain that
structure is not considered a SAN, but the fabric can be used
way for some time. Most drive suppliers expect to continue sup-
to greatly expand near-box storage far beyond traditional
porting parallel SCSI and ATA drives for enterprise customers
parallel SCSI applications. In some cases, SAS is also finding
for many years to come. However, these implementations are
its way into remote storage subsystems, especially in NAS-
not without problems, especially as storage systems expand far
based implementations.
nicate through FC switches before reaching the external storage
beyond their original intent. Some implementations are already
experiencing problems with the limits of parallel data transmission and these are becoming increasingly difficult to manage
as data transmission speeds increase. Other implementations
have had problems related to scalability, as demands on their
3
SAS and SATA Team Up for the Enterprise
Enterprise class SATA drives are available now. Advancements
in SATA drives oriented specifically to the enterprise have resulted in improved drive reliability, as confirmed in server and video
security applications requiring 24x7 duty cycles. Active vibration
correction technologies have solved the problem created when
SATA in a SAS Infrastructure –
Enterprise Solutions for Tomorrow
SAS Infrastructure Supports Both
SAS and SATA Drives
vibrations from one drive impact the tracking of an adjacent
The SAS infrastructure supports both SAS and SATA drives.
drive. Also, the new generations of SATA 3.0 Gbps drives with
The SAS interface was designed from the outset as a superset
Native Command Queuing (NCQ) allow an onboard processor to
of the SATA interface. SATA drives can plug into a SAS connec-
reorder I/O reads and writes. This minimizes head movement
tor, though the opposite is not true. No bridging is required.
and the amount of time the head spends waiting for the platter
There are no jumpers to select and no software to change.
to spin around to the proper sector. While NCQ is not as powerful
The SAS protocol provides a discovery capability that allows
as the queuing found on FC or future SAS drives, the market is
the host controller to sense whether the drive attached to the
accepting NCQ as adequate for many mainstream server tasks,
system is a SAS or a SATA drive and will adjust accordingly.
with the exception of heavily loaded, highly random database
workloads typically performed by larger servers.
Flexible Scalability
These additional drive improvements have greatly enhanced data
For the first time in the evolution of storage technology there
reliability and availability and will expand the acceptance of SATA
will be the opportunity to establish storage infrastructure in
drives in mission-critical enterprise applications. Although the
the enterprise that is capable of growing in two directions –
enterprise version of these drives may be priced at a premium
affordable yet reliable capacity or high performance. SAS
(25-40 percent higher) relative to their commoditized desktop
expanders allow for systems with either SAS or SATA drives to
brethren, in most cases they offer a lower priced alternative in
scale greatly, and the dual-port nature of the SAS infrastructure
enterprise environments. The ability to run with existing SATA
provides a failover structure that works independently of the
software means that no new device drivers are required. All
drive type being used.
mapping of operating system I/O calls from legacy software
Native SATA has an inherent one-to-one association with the
drivers to the new serial interface is done on the controller card.
host, which does not lend itself to a multi-host configuration.
The SATA tunneling mechanism provided with the SAS protocol
allows a SATA device to operate without knowing the host from
which a request came. The SATA one-to-one association is managed at the end-point that connects to the SATA drive – another
advantage of the point-to-point nature of both SAS and SATA.
The value of stored data changes over time within an enterprise.
Concepts like Information Life-cycle Management (ILM) address
the dynamic nature of data. Information that one day is critical
for stocking the shelves with the right items in the right location
at the right time, may now only be useful for business analysis,
historical references or regulatory compliance.
The SAS infrastructure delivers compelling value to this challenging enterprise environment by allowing storage enclosures
to be re-provisioned within the enterprise as the demands upon
these data systems change. The high-performance ERP applications of today may use SAS drives initially to address I/O
performance requirements. As data accumulates and newer
and faster storage subsystems are acquired to satisfy increasing
performance demands, SAS enclosures can be re-provisioned
with SATA drives to expand the available storage needed for
regulatory compliance.
4
SAS and SATA Team Up for the Enterprise
SAS + SATA Configuration Examples
Figure 1 – SAS System Expansion Capabilities
SAS System Expansion Capabilities
Ds
r D er
o
sts and
Ho Exp
8
12 ge
to E d
Up per
SAS has the ability to address upwards of
Dis
r
kD
16,000 devices per port through low-cost
ive
expansion devices called expanders. Simple
expanders are referred to as edge expanders
and allow up to 128 devices to be addressed
H
t
os
without the cost of complex routing tables.
Edge expanders are often cascaded to provide
the required number of ports to support a
ps
Ex der
e
dg pan
8 E t Ex
2
1 u
to n o
Up er Fa
p
large numbers of drives contained within
an enclosure or rack-mounted shelf. More
sophisticated implementations require fanout
expanders that route traffic between the various
edge expanders and provide for much greater
expansion capabilities.
Figure 2 – SAS Performance and Availability
Se
SAS Performance and Availability
68
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Because SAS allows ports to be aggregated,
high-bandwidth connections between the host
and storage enclosures give SAS the bandwidth
S
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erv
to support large numbers of drives. The 4-port
68
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te
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and provides an aggregate bandwidth to the host
TA
SA isks
D
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implemented using standard cabling techniques
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of 24 Gbps. The dual-port nature of SAS also
provides high-availability failover capabilities,
providing access to all storage devices in the
on
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ct
s
ion
case of a failed host. Either SAS or SATA drives
may be attached directly to host controller
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Dis
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devices or addressed through expanders.
5
SAS and SATA Team Up for the Enterprise
Figure 3 – Spoke and Hub Infrastructure
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Spoke and Hub Infrastructure
The spoke and hub infrastructure achieves cost savings based on
The SAS infrastructure can be deployed in both the central
tiered performance. The central IT office, which houses the core
and remote offices to provide a common storage platform.
infrastructure, requires high performance and high reliability.
Both office types can use the same storage infrastructure,
In addition to providing backup and data sharing for the remote
but overall cost savings are realized by augmenting the infra-
offices, key systems such as purchasing are controlled from this
structure with the drive type suited to each (SAS for central
site. These applications require SAS drives for maximum speed
and SATA for remote).
and reliability.
Imagine a remote office that houses anywhere from 2 to 1,000
employees and supports only the needs of that particular office.
It backs up and consolidates data at a central hub and can tolerate lower MTBF per drive so can use RAID. SATA drives satisfy
these requirements and provide additional cost savings because
they offer higher capacity per drive than SCSI/SAS drives.
6
e
Conclusion
Contact Information
For the first time, IT buyers can implement a single storage infrastructure that offers both flexibility and scalability. Its ability to
uniquely serve the high-performance needs of the enterprise with
SAS drives and also the high-capacity needs with enterprise-class
SATA storage allows it to scale flexibly as enterprise needs change.
This flexibility, combined with efficiencies provided by combinations of
SAS and SATA drives that have common components (cables, connec-
Harry Mason
LSI Logic Corporation
hmason@lsil.com
tors, enclosures and backplanes), will allow the enterprise to meet
new demand without substantially growing existing IT budgets.
Scott Peiffer
Intel Corporation
scott.t.peiffer@intel.com
Hubbert Smith
Western Digital Corporation
hubbert.smith@wdc.com
7
www.lsilogic.com
www.intel.com
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