[gentoo-user] Re: recovering RAID from an old server

[Francesco Talamona]

On Saturday 20 February 2010, Iain Buchanan wrote:
> On Sat, 2010-02-20 at 10:46 +0100, Francesco Talamona wrote:
> > > Should I be able to mount them automatically and let the SW RAID
> > >  module sort it out or do I have to know how they're tied
> > > together beforehand?
> > >
> > > md: looking for a shared spare drive
> > > md100: no spare disk to reconstruct array! -- continuing in
> > > degraded mode
> > > md: recovery thread finished ...
> > > md: hde5 [events: 000003a5]<6>(write) hde5's sb offset: 273024
> > > md: hdg5 [events: 000003a5]<6>(write) hdg5's sb offset: 273024
> > > XFS mounting filesystem md(9,100)
> > > Ending clean XFS mount for filesystem: md(9,100)
> > >
> > > The partitions look like:
> > > 9   100     546112 md100
> > >    9   101     273024 md101
> >
> > It seems it has correctly mounted its partition... Can't you find
> > it?
>
> This is with the server recovery console, which is basically just a
>  web page.  No shell access.  There's not much I can do to get at
>  md100 and md101 (is this what software RAID devices usually appear
>  as?)
>
> > I have the feeling that you are messing it up. If I understand it
> > correctly the server has an hardware RAID controller, that has to
> > be managed via its drivers.
>
> I think it's software RAID.  There is no RAID controller AFAICT.  All
>  4 drives are visible to the BIOS as Primary and Secondary Master and
>  Slaves.

This isn't a proof: most hardware RAID are proprietary software 
solutions pretending to be hardware. Linux without the driver can't see 
the logical volume and shows all the physical drives.

You should do some research about that server hardware... Aren't snap 
equipped with PERC controller?.

> > Another thing can come very useful: we once had a similar problem,
> > we ended up borrowing one identical disc from another running
> > server to put the array back online, we recovered our data, then
> > restored the other server's array.
>
> That's a possibility given what I can find on Google, however these
>  are few and far between, so I'd have to find someone willing to send
>  their drive to me (or vice versa) or send me the OS, which
>  overlandstorage doesn't like!

What happens if you physically remove the drive marked as bad?

You may image it for backup, then format it at low level, then put it 
back in place as if it was brand new. Or add a similar disk to be 
considered spare by the controller (given that it is looking for a spare 
disk in first instance).

Most controller have automated procedures to manage failures, disk swaps 
and so on.

For this reason you can't be sure that the inspection operations you are 
doing are read only. Unless the drives are attached to another machine 
with a trusted OS doing nothing on its own.

The ideas given above may let you to waste all of your data, be very 
careful and patient.

Good luck.
	Francesco

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