On Tue, Mar 09, 2010 at 01:16:01PM +0300, Michael Tokarev wrote:
> Karel Zak wrote:
> > # mdadm --create /dev/md8 --level=5 --raid-devices=4 /dev/sdb{1,2,3,4}
>
> That's 3-disk stripe size with default 64Kb chunk size, which makes
> 3x64=320KiB - the number to which everything should be aligned.
>
> > # fdisk -lcu /dev/md8
> >
> > Disk /dev/md8: 1572 MB, 1572667392 bytes
> > 2 heads, 4 sectors/track, 383952 cylinders, total 3071616 sectors
> > Units = sectors of 1 * 512 = 512 bytes
> > Sector size (logical/physical): 512 bytes / 4096 bytes
> > I/O size (minimum/optimal): 65536 bytes / 65536 bytes
>
> And here we go: fdisk does not see the right number: nothing
> is dividable by 3.
>
> []
> > # cat /sys/block/md8/md8p{1,2}/alignment_offset
> > 0
> > 0
>
> And that's where the issue is. md does not {sup,re}port all
> this stuff yet.
>
> This is what I'm talking about.
Note that I have 2.6.31.12-174.2.22.fc12.x86_64 kernel on my laptop.
It would be better for serious tests to use 2.6.33.
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
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