Re: ATA 4 KiB sector issues.

[Karel Zak <kzak@redhat.com>]

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@redhat.com>