[parted-devel] [PATCH 6/6] libparted: fix optimal IO alignment

[Phillip Susi]

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On 12/19/2012 11:45 AM, Jim Meyering wrote:
> Phillip Susi wrote:
>> Sure, take a 4 disk raid5 with 256k stripe factor.
> 
> Am I misunderstanding something? 256k is both smaller than 1MiB and
> *is* a power of 2. I was asking if you'd seen values *not* like
> that.

A 4 disk raid 5 with 256k stripe factor uses 256k from each of 3 disks
( 4th is parity ), giving a stripe width and thus an optimal alignment
of 768k.

> I guess it comes down to whether there are systems that return
> bogus values there, and whether there are systems that return legit
> values smaller < 1MiB, like I was asking about above.

I'm not aware of any known bugs where the kernel returns inappropriate
values, but there are plenty of raid configurations that do use < 1MiB
and/or non power of two alignments.


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