Re: ffs can't find superblock

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Feb 04, 2011 at 10:37:04PM +0000, David Laight wrote:
> On Sat, Feb 05, 2011 at 12:25:57AM +0200, Alan Barrett wrote:
> > On Thu, 03 Feb 2011, mortee wrote:
> > > $ sudo fsck_ffs /dev/rwd3a
> > > ** /dev/rwd3a
> > > BAD SUPER BLOCK: CAN'T FIND SUPERBLOCK
> > > 
> > > I've already tried specifying a few other possible superblock backup
> > > locations using -b, but it reports wrong magic number for each one tried.
> > 
> > If the disklabel is correct, you could run newfs(8) with the "-N"
> > flag to get a list of of alternative superblock locations:
> > 
> >     /sbin/newfs -N -V4 /dev/rwd3a
> > 
> > Then try those locations one by one with "fsck -b".
> 
> I wouldn't run fsck on that filesystem, it might remove any chance
> of recovering some of the data.
> You need something non-destructive that tries to recover files to
> a different disk.

With -N it's not destructive; it only prints filesystem parameters without
writing anything to disk.
This is one way to get a complete list of alternate superblocks.

(to be safe you can also run it as regular user, group operator.
this way newfs will be denied write access to disk)

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--