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Old 02-20-2010, 02:22 PM
Andrea Conti
 
Default recovering RAID from an old server

> md: bind<hdg2,1>
> md: bind<hde2,2>
> md: bind<hda2,3>
> raid1: raid set md100 active with 3 out of 4 mirrors

> md: bind<hdg5,1>
> md: bind<hde5,2>
> md: bind<hda5,3>
> raid1: raid set md101 active with 3 out of 4 mirrors

AFAICT this is all you need to know -- you definitely have two software
(mdraid) RAID 1 volumes:

md100 with hda2, hde2 and hdg2 as members
md101 with hda5, hde5 and hdg5 as members

Both arrays seem to have lost a member (I guess hdc2 and hdc5 respectively).

Honestly I don't know what is the point of running RAID1 volumes with
four mirrors, but that seems to be the way it was configured.

I would suggest that you take a *single* disk (let's say hdg) out of the
thing and hook it up to a fully functional Gentoo system with mdraid
(and of course XFS) compiled in the kernel and sys-fs/mdadm installed.

Then you can bring up each RAID volume in degraded state from the single
mirror:

#mdadm -A /dev/md100 -R /dev/hdX2
#mdadm -A /dev/md101 -R /dev/hdX5

(substiture hdX with the actual device name of the transplanted disk; in
any case mdadm has a very useful man page)

At this point you should be able to mount md100 and md101 *read-only*
and salvage any data you need.

Andrea
 
Old 02-20-2010, 10:22 PM
Neil Bothwick
 
Default recovering RAID from an old server

On Sat, 20 Feb 2010 16:22:51 +0100, Andrea Conti wrote:

> > md: bind<hdg5,1>
> > md: bind<hde5,2>
> > md: bind<hda5,3>
> > raid1: raid set md101 active with 3 out of 4 mirrors
>
> AFAICT this is all you need to know -- you definitely have two software
> (mdraid) RAID 1 volumes:

Agreed, however Iain also said that he tried to mount individual
partitions and this failed. This should work with RAID1, so I wonder if
something else is at work here; either some sort of logical volumes or a
weird filesystem in use.


--
Neil Bothwick

Heisenberg's Uncertainty Principle: The location of all objects cannot be
known simultaneously. Corollary: If a lost thing is found, something else
will disappear.
 
Old 02-21-2010, 07:10 AM
Andrea Conti
 
Default recovering RAID from an old server

> Agreed, however Iain also said that he tried to mount individual
> partitions and this failed. This should work with RAID1

Only if you force the filesystem type (i.e. mount -t xxx, or use
mount.xxx directly).

However, while I know this works with ext2/ext3/ext4, I have no idea if
xfs is also smart enough to ignore the raid superblock and mount the
filesystem anyway in this case.

andrea
 
Old 02-21-2010, 11:05 AM
Iain Buchanan
 
Default recovering RAID from an old server

On Sat, 2010-02-20 at 16:22 +0100, Andrea Conti wrote:

> AFAICT this is all you need to know -- you definitely have two software
> (mdraid) RAID 1 volumes:
>
> md100 with hda2, hde2 and hdg2 as members
> md101 with hda5, hde5 and hdg5 as members
>
> Both arrays seem to have lost a member (I guess hdc2 and hdc5 respectively).
>
> Honestly I don't know what is the point of running RAID1 volumes with
> four mirrors, but that seems to be the way it was configured.

strange, I'm pretty sure I didn't configure it like this - however it
has an inbuilt snapshot feature so maybe that's what the mirrors are
for...

I'm having some luck chasing up the original CDs so I think I'll try
that first.

thanks
--
Iain Buchanan <iaindb at netspace dot net dot au>

If it smells it's chemistry, if it crawls it's biology, if it doesn't work
it's physics.
 
Old 02-21-2010, 02:32 PM
Neil Bothwick
 
Default recovering RAID from an old server

On Sun, 21 Feb 2010 09:10:41 +0100, Andrea Conti wrote:

> > Agreed, however Iain also said that he tried to mount individual
> > partitions and this failed. This should work with RAID1
>
> Only if you force the filesystem type (i.e. mount -t xxx, or use
> mount.xxx directly).

Not in my experience.

> However, while I know this works with ext2/ext3/ext4, I have no idea if
> xfs is also smart enough to ignore the raid superblock and mount the
> filesystem anyway in this case.

The RAID superblock is at the end of the filesystem, to avoid any
conflicts with the filesystem superblock.


--
Neil Bothwick

Never get into fights with ugly people because they have nothing to lose.
 
Old 02-22-2010, 04:18 AM
Andrea Conti
 
Default recovering RAID from an old server

> The RAID superblock is at the end of the filesystem, to avoid any
> conflicts with the filesystem superblock.

It can be either at the start, at the end or even 4K into the device,
depending on which format (metadata revision) is used. In this case I
suppose it's 0.90, which is stored at the beginning.

andrea
 

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