On Mon, 12 Feb 2007, Chris Csanady wrote:
[ ... ]
> Am I missing something?
How do you guarantee that the disk driver and/or the disk firmware doesn't
reorder writes ?
The only guarantee for in-order writes, on actual storage level, is to
complete the outstanding ones before issuing new ones.
This is true for NCQ with SATA, but SCSI also supports ordered tags,
so it should not be necessary.
At least, that is my understanding.
Except that ZFS doesn't talk SCSI, it talks to a target driver. And that
one may or may not treat async I/O requests dispatched via its strategy()
entry point as strictly ordered / non-coalescible / non-cancellable.
See e.g. disksort(9F).
FrankH.
Chris
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