Re: 16 HDDs too much for RAID6?

[Andre Noll <maan@systemlinux.org>]

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On 10:01, Lars Täuber wrote:
> Here we have another problem with our RAID6 and 16 HDDs:
> 
> monosan:~ # mdadm -V
> mdadm - v2.6.2 - 21st May 2007
> monosan:~ # mdadm -C /dev/md4 -l6 -n 16 -x 0 /dev/dm-*
> mdadm: /dev/dm-0 appears to be part of a raid array:

Run
	mdadm --zero-superblock /dev/dm-0

before creating the array to get rid of these.

> monosan:~ # mdadm --detail --scan| fgrep md4 >> /etc/mdadm.conf 

Please post your /etc/mdadm.conf

> monosan:~ # mdadm -A /dev/md4
> mdadm: WARNING /dev/dm-9 and /dev/dm-8 appear to have very similar superblocks.
>       If they are really different, please --zero the superblock on one
>       If they are the same or overlap, please remove one from the
>       DEVICE list in mdadm.conf.

Are you sure dm-8 and dm-9 are different devices?

	pvdisplay /dev/dm-9; pvdisplay /dev/dm-8

should tell you.

> This happens _always_ when the arreay is reassembled. The actual
> devices with the duplicated superblocks differ sometimes.

If I read the code correctly it means that the two devices have
identical superblocks, the same event count and the same minor number,
so mdadm thinks dm-8 and dm-9 are overlapping partitions.

> Are 16 drivesmda too much for RAID6?

No, raid6 supports up to 254 devices (there are other reasons for
not using too many devices for raid6 though).

Andre
-- 
The only person who always got his work done by Friday was Robinson Crusoe

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