On 10/30/2009 12:53 AM, Martin K. Petersen wrote:
"Doug" == Douglas Gilbert<dgilbert@xxxxxxxxxxxx> writes:
Doug> And if both are supported by the logical unit, the patch prefers
Doug> UNMAP?
Yes.
SBC states that if the device reports MAXIMUM UNMAP LBA COUNT> 1 and
MAXIMUM UNMAP DESCRIPTOR COUNT> 1 then the device supports UNMAP. And
in that case that's what I'll issue. In all other cases I'll send out
WRITE SAME(16). I believe that approach is what's currently considered
best practice.
This sounds like the correct thing to do.
We should at the same time try to unify the file system mount options so
we roll out the testing in a careful way.
Specifically, I would suggest that we default to "not" issuing discards
by default and that we try to use the same mount option for any file
system that supports barrier discards. My worry is that we will fry
SSD's (like the reported issues with the Intel SSD's and Windows 7) or
have horrific performance on arrays that are not tuned for fine grained
discards :-)
Ric
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