Re: not enough operational mirrors

[NeilBrown <neilb@suse.de>]

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On Mon, 22 Sep 2014 10:17:46 -0700 Ian Young <ian@duffrecords.com> wrote:

> I forced the three good disks and the one that was behind by two
> events to assemble:
> 
> mdadm --assemble --force /dev/md0 /dev/sda2 /dev/sdb2 /dev/sdc2 /dev/sde2
> 
> Then I added the other two disks and let it sync overnight:
> 
> mdadm --add --force /dev/md0 /dev/sdd2
> mdadm --add --force /dev/md0 /dev/sdf2
> 
> I rebooted the system in recovery mode and the root filesystem is
> back!  However, / is read-only and my /srv partition, which is the
> largest and has most of my data, can't mount.  When I try to examine
> the array, it says "no md superblock detected on /dev/md0."  On top of
> the software RAID, I have four logical volumes.  Here is the full LVM
> configuration:
> 
> http://pastebin.com/gzdZq5DL
> 
> How do I recover the superblock?

What sort of filesystem is it?  ext4??

Try "fsck -n" and see if it finds anything.

The fact that LVM found everything suggests that the array is mostly
working.  Maybe just one superblock got corrupted somehow.  If 'fsck' doesn't
get you anywhere you might need to ask on a forum dedicated to the particular
filesystem.

NeilBrown


> 
> On Sun, Sep 21, 2014 at 10:47 PM, NeilBrown <neilb@suse.de> wrote:
> > On Sun, 21 Sep 2014 22:32:19 -0700 Ian Young <ian@duffrecords.com> wrote:
> >
> >> My 6-drive software RAID 10 array failed.  The individual drives
> >> failed one at a time over the past few months but it's been an
> >> extremely busy summer and I didn't have the free time to RMA the
> >> drives and rebuild the array.  Now I'm wishing I had acted sooner
> >> because three of the drives are marked as removed and the array
> >> doesn't have enough mirrors to start.  I followed the recovery
> >> instructions at raid.wiki.kernel.org and, before making things any
> >> worse, saved the status using mdadm --examine and consulted this
> >> mailing list.  Here's the status:
> >>
> >> http://pastebin.com/KkV8e8Gq
> >>
> >> I can see that the event counts on sdd2 and sdf2 are significantly far
> >> behind, so we can consider that data too old.  sdc2 is only behind by
> >> two events, so any data loss there should be minimal.  If I can make
> >> the array start with sd[abce]2 I think that will be enough to mount
> >> the filesystem, back up my data, and start replacing drives.  How do I
> >> do that?
> >
> > Use the "--force" option with "--assemble".
> >
> > NeilBrown


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