16 HDDs too much for RAID6?

["Lars Täuber" <taeuber@bbaw.de>]

Hallo!

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:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-1 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-10 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-11 appears to contain an ext2fs file system
    size=-2147483648K  mtime=Thu Jan  1 01:00:00 1970
mdadm: /dev/dm-11 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-12 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-13 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-14 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-2 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-3 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-4 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-5 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-6 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
mdadm: /dev/dm-7 appears to be part of a raid array:
    level=raid6 devices=15 ctime=Wed Feb 13 10:38:52 2008
Continue creating array? y
mdadm: array /dev/md4 started.

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

monosan:~ # mdadm -S /dev/md4
mdadm: stopped /dev/md4

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.

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

Are 16 drives too much for RAID6?

Thanks
Lars

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