Re: [PLUG] Ninja repair of a XFS volume

[Julien Vehent <julien@linuxwall.info>]

On 01/27/2011 09:45 PM, Rich Freeman wrote:
> On Thu, Jan 27, 2011 at 6:54 PM, Julien Vehent<julien@linuxwall.info>  wrote:
> > The normal move would be to restart the system in single user, or using a
> > live cd, and run a xfs_repair on /dev/sda.
>
> Well, the key is to not have sda mounted.  If that is your root
> partition, then a liveCD/etc may be your only option.  Or, if you can
> get your virtual hosting provider to send you a disk image and take a
> fixed one back you can easily fix it with a loopback device/etc.

I don't get that kind of service for a 15euros/months hosting service 
(dedibox by online.net if you're curious).

> > So, question is: does anyone know a way to repair/fix that XFS filesystem by
> > hand ?
> > Any low-level XFS manipulation tool that could help ?
>
> I would think that any approach would not work safely if the device is
> mounted.  The OS caches critical control structures in RAM, so once
> you fix what is on disk they could be overwritten by inconsistent
> metadata the next time there is a flush.
>
> If the device isn't mounted then the usual xfs repair tools will fix
> the problem.  If the device is mounted then there isn't much you can
> do, unless you build some kind of a kernel module with your own custom
> xfs code that allows online fixing (I'm sure a patch for that would
> make everybody happy).

That's not happening, I can't write xfs code.

However, somebody on serverfault proposed that I migrate / in a tmpfs on 
the fly, the migrate the root and unmount my volume. That's crazy enough 
(on a production system), I might try it.
Note that when I say production, It's just websites of friends and 
related and a few other services.

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