Technical information

HGST Ultrastar C15K600 Hard Disk Drive Specification
301
20.1.3
Overlapped Commands
The drive does not perform any overlapped command checking.
20.1.4
Command Processing During Execution of Active I/O
Process
When the target is not executing any I/O processes, a new I/O process is permitted to execute (unless execution is
prevented by another internal target condition listed in 20.1.1 "Priority of SCSI Status Byte Reporting").
If an active I/O process exists when the target receives a new command, then the target determines if:
- the command is permitted to execute
- the command is added to the queue
- Queue Full status is to be returned
- Busy status is to be returned
If an active I/O process exists when the target receives a new command, then the target determines how the new
command should be handled based on the following rules:
- Check Condition status is returned with sense key set to Logical Unit Not Ready if:
- the startup operation or a format operation is active. See Command Processing During Execution of Active I/O
Process for the exact conditions which cause this response.
Note: If a Unit Attention is pending when this condition exists, the sense key is set to Unit Attention rather than
Logical Unit Not Ready since Unit Attention has a higher reporting priority (see 20.1.4 "Command Processing During
Execution of Active I/O Process")
- The command is permitted to execute if:
- the command is a priority command (see Concurrent I/O Process the conditions to execute concurrently are met
(see 20.1.1 "Priority of SCSI Status Byte Reporting")
- The command is added to the queue if:
- any I/O process already exists at the target, and
- this is not an incorrect initiator connection.
- Queue Full status is returned if:
- the command would otherwise be added to the queue (according to the rules described above), but all slots in
the queue are full, or the command would otherwise be added to the queue (according to the rules described
above), but all of the available queue slots not reserved for use by another initiator are full, or a Format Unit
command was previously queued but has not yet begun execution, or the target is in a Degraded Mode (see
"Degraded Mode") and a Start Unit command was previously queued but has not yet begun execution.
- Busy status is never returned on SCSI or FCAL. BUSY status is returned on SAS if more than 64 unique
Initiators send frames to the drive since the last POR. In that case, BUSY status in only returned for Initiators
above and beyond the first 64.