queue depth help!!
Hello James,
Case :queue depth=1
On issuing a scsi command write, does the data needs to be written succesfully
to disk before issuing a scsi response. Is there a chance that the previous command's data is still cached on scsi controller and the next command issued is executed.
Please let me know if there are any good tools for scsi analyzer.
Thanks
Jay
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===== Original Message From James Bottomley <[email protected]>
=====
Quoted 2 lines · jshankar
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if the scsi target queue depth is 1, does it mean that i can handle only
one
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outstanding command at a time.
Yes
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Does it mean if another command is issued( queue depth=1), it has to wait
till
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the previous command is done.
Yes.
The mid-layer will start the queued command as soon as the one occupying the device returns...this is often why untagged devices actually set their depth to 2 so they can have another command all prepared and ready to roll as soon as the in-progress one returns.
James
Quoted 5 lines · jshankar
On issuing a scsi command write, does the data needs to be written succesfully
to disk before issuing a scsi response. Is there a chance that the previous command's data is still cached on scsi controller and the next command issued is executed.
That depends on the drive cache setting. For a write back cache, no--status will be sent before the command reaches the medium (as long as the FUA bit isn't set); for all other cache settings, yes.
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Please let me know if there are any good tools for scsi analyzer.
I don't actually have one of these, so I'll let others answer...
James