Technical information

HGST Ultrastar C15K600 Hard Disk Drive Specification
312
20.2
Priority Commands
Certain SCSI commands always execute without returning a Busy Status or Reservation Conflict Status in response
to the command. These commands are
- Inquiry
- Request Sense
- Report LUNs
- Test Unit Ready
These commands are executed prior to attempting to complete the execution of any other pending command in the
queue. These commands are never queued.
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