Re: ATA 4 KiB sector issues.

[Michael Tokarev]

Dave Chinner wrote:
> On Tue, Mar 09, 2010 at 01:16:01PM +0300, Michael Tokarev wrote:
>> Karel Zak wrote:
>>> I did almost all my tests with scsi_debug or MD RAID0 on scsi_debug.
>>> It works as expected.
>> Actually, for raid0, the alignment is questionable.  Should it be a
>> multiple of chunk size or whole stripe size?  I'm not sure, both ways
>> has bad and good sides..  But if it is the latter, the same issues
>> pops up again: do a 3-disk raid0 and you'll have to align to 3*2^N.
> 
> Yes, alignment is still needed, especially for filesystems that can
> do stripe unit aligned allocation like XFS. If you don't align the
> filesystem properly, all the data IO will be mis-aligned to the
> underlying disks and stripe unit sized IO will hit multiple disks
> rather than just one....

I understand alignment is needed, the question is if the alignment
should be to chunk size or full-stripe size.  In neither case it
will be bad for underlying disks.

/mjt
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