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Commands which cause an OVERLAPPED COMMANDS ATTEMPTED error. See Section 11.1.3 ,
“Incorrect Initiator Connection" on page 194.
11.3.1 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.
11.3.2 Tagged queuing
Commands with a tag message are saved in the command queue. Queued commands will be reordered
by the drive defined rule. See Section 11.4, “Command reordering” on page 206 for details.
11.3.3 Untagged queuing
The drive supports queuing one I/O process from each initiator. If the drive receives an untagged I/O pro-
cess while executing an I/O process from a different initiator, the untagged I/O process may be queued.
The drive treats untagged I/O processes as though they were received with Simple Queue Tag messages
for purposes of queuing.
11.3.4 Command queuing rule
Commands can be received during an active I/O process if the Bus is free. I/O processes of READ(6),
READ EXTEND(10), WRITE(6) and WRITE EXTEND(10) can be active at the same time. See
Section 11.5 , "Concurrent I/O Process" on page 206 for details.
11.3.5 QUEUE FULL status
This status is returned when a SIMPLE, ORDERED, or HEAD OF QUEUE tag message is received and
the command queue is full. The I/O process is not placed in the command queue. Since one queue ele-
ment is reserved for each initiator, any untagged command that does not cause Incorrect Initiator
Connection will not cause QUEUE FULL status.
11.3.6 Device behavior on Command queuing
1.
Initiators must send a Queue tag immediately after the IDENTIFY message in MESSAGE OUT
phase just after SELECTION. Targets send a SIMPLE queue tag immediately after the Identify mes-
sage in MESSAGE IN phase just after RESELECTION.
2.
Each initiator can issue either a tagged command or an untagged command exclusively at the same
time. Other initiators can exist which operate mutually exclusively with tagged or untagged com-
mands.
3.
When DQue (Mode Page A) is set to1, if an initiator issues a tagged command, the drive returns
MESSAGE REJECT message (07h) and receives that command as an untagged command.
4.
Queue Tag number does not affect the order of execution.
5.
If an initiator issues a command with a queue tag which is the same as the current I/O process or
queued I/O process, the drive may return Incorrect Initiator connection. See Section 11.1.3 ,
“Incorrect Initiator Connection" on page 194.
6.
A series of linked commands are a single I/O process and are assigned the queue tag established in
the initial selection. A command received with a HEAD OF QUEUE tag message shall not suspend a
series of linked commands for which the drive has begun execution.
7.
If DQue is changed to 1 while queued commands exist, all queued commands for the all initiators
will be aborted. All future commands received from any initiator with a queue tag will be processed
Ultrastar 146Z10 hard disk drive specifications
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