On Tue, Mar 09, 2010 at 01:16:01PM +0300, Michael Tokarev wrote:
quoted text
> 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.

 Well, the same setup with 2.6.34-0.9.rc0.git13.fc14.x86_64:

 # fdisk -luc /dev/sdb

 Disk /dev/sdb: 2621 MB, 2621440000 bytes
 255 heads, 63 sectors/track, 318 cylinders, total 5120000 sectors
 Units = sectors of 1 * 512 = 512 bytes
 Sector size (logical/physical): 512 bytes / 4096 bytes
 I/O size (minimum/optimal): 4096 bytes / 32768 bytes
 Disk identifier: 0x77fbab55

 Device Boot         Start         End      Blocks   Id  System
 /dev/sdb1            2048     1026047      512000   83  Linux
 /dev/sdb2         1026048     2050047      512000   83  Linux
 /dev/sdb3         2050048     3074047      512000   83  Linux
 /dev/sdb4         3074048     4098047      512000   83  Linux


 # mdadm --create /dev/md8 --level=5 --raid-devices=4 /dev/sdb{1,2,3,4}


 # fdisk -luc /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


 # cat /sys/block/md8/queue/{minimum,optimal}_io_size 
 65536
 65536

quoted text
> >  # 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.

 Hmm...

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
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