Re: recovering a mirrored arry.

[Robin Hill <robin@robinhill.me.uk>]

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On Fri Feb 05, 2010 at 07:50:44PM +0100, Keld Simonsen wrote:

> On Fri, Feb 05, 2010 at 04:25:02PM +0000, Kristleifur Daðason wrote:
> > On Fri, Feb 5, 2010 at 1:19 AM, Keld Simonsen <keld@keldix.com> wrote:
> > > On Wed, Feb 03, 2010 at 03:57:58AM +0100, Keld Simonsen wrote:
> > > Hi
> > >
> > >
> > > can anybody help me with this? I am stuck with recovering my system here.
> > > is it a sensible thing ro do?
> > >
> > > best regards
> > > keld
> > >
> > >> Hi
> > >>
> > >> I got 2 arrays in error of the raid10 type.
> > >>
> > >> I think this is because my motherboard died, and then the fs were
> > >> corrupted.
> > >>
> > >> My thoughts were that actually one of the copies could be correct.
> > >> So I would like to try out the consistency of each part of the raid10
> > >> (it is 2-partition arrays), and then if I find one that is consistent, then
> > >> resync the faulty one with the good one.
> > >>
> > >> How do I do this?
> > >>
> > >> it seems that I cannot just assemble an array with a missing part.
> > >> If I assemble the full array, is there then a risk of the bad one
> > >> corrupting the good one? And can I declare one of the disks faulty
> > >> then test the other one, then declare nbr 2 disk for faulty and
> > >> declare the first one as good?
> > >>
> > >> I dont see anything on the wiki on this.
> > >>
> > >> best regards
> > >> keld
> > > --
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> > >
> > 
> > 
> > I wish I could help more, but check out this from the mdadm man page:
> > 
> >        To create a "degraded" array in which some devices are missing,
> > simply give
> >        the word "missing" in place of a device name.  This  will
> > cause  mdadm  to
> >        leave  the  corresponding  slot  in  the array empty.  For a
> > RAID4 or RAID5
> >        array at most one slot can be "missing"; for a  RAID6  array
> > at  most  two
> >        slots.   For a RAID1 array, only one real device needs to be
> > given.  All of
> >        the others can be "missing".
> 
> I tried missing, but mdadm said that it could not find missing as a device,
> for assemble mode.
> 
No, as the manual page says, "missing" is only used for creating an
array, not for assembling.

If you only give a single device in the assemble command then mdadm
_ought_ to only use that to assemble the array.  I'm not 100% sure that
it does it though - probably worth testing with loopback devices first.

The other option would be to use "create" to create new degraded arrays
containing only the single disks.  You'd need to make sure you used the
same settings as for the old array though.

Alternately, physically disconnect the drives in turn and assemble the
array with the single drive.

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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