Ultrastar C10K600 OEM Specification

20.3 Command Queuing

When the initiator specifies that the drive shall disable command queuing, the initiator must send only untagged commands.

When the initiator specifies that the target shall enable command queuing, the initiator may send either tagged or untagged command, but shall not use both at the same time.

The following commands are never queued.

• Priority Commands (i.e.: Request Sense and Inquiry)

• Commands for an invalid LUN.

20.3.1 Queue Depth

Any initiator can queue at least one command at any time irrespective of the actions of any other initiators in the system. A single initiator may queue up to 128 commands, if no other initiator has more than one command in the queue, although at times this maximum may be reduced as the drive can reserve command blocks for internal use.

20.3.2 Queue Full Status

The drive will respond with QUEUE FULL status to a SCSI command when all queue slots are utilized. The SCSI command is not placed in the command queue under this condition.

20.3.3 Termination of I/O Processes

Normal termination of I/O processes occurs when the target returns SCSI status. I/O processes may also be terminated by the following:

• An ABORT TASK terminates the specified I/O process from the issuing initiator

• An ABORT TASK SET terminates all I/O processes from the issuing initiator

• A CLEAR TASK SET, TARGET RESET or reset terminates all I/O processes from all initiators

20.4 Command Reordering

Command reordering is supported when enabled by the Queue Algorithm Modifier in mode page 0A (see 18.10.9, “Mode

Page 0A (Control Mode Page Parameters)” on page 150.

20.5 Concurrent I/O Process

Concurrent command are always allowed to execute concurrently with non-priority commands. A second priority command received while a priority command is being executed is put at the head of the command queue.

• WRITE commands when another WRITE command is an active I/O process

• READ commands when another READ command is an active I/O process

When a concurrent command ends in CHECK CONDITION status, the QErr bit on the Mode Page 0Ah will determine how other active I/O processes from the same initiator for that drive will be handled.

20.6 Write Cache

If the WCE (Write cache enable) bit is 1, the drive returns Good Status and closes the connection immediately after receiving the data of the last sector before actually writing the data onto the media.

If the drive detects an error after it returns a Good Status, the drive sets a Deferred Error (Error Code of sense data = 71h) and a following command will be returned with Check Condition and the Contingent allegiance condition is established. Under the

Contingent allegiance condition all queued processes including commands from other initiators are suspended.

HGST Ultrastar C10K600 (SAS) Hard Disk Drive Specification

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