Re: Need help to recover root filesystem after a power supply issue

Eric Sandeen
2019-07-10T13:26:17Z

On 7/10/19 4:56 AM, Andrey Zhunev wrote:
> Hello All,
>
> I am struggling to recover my system after a PSU failure, and I was
> suggested to ask here for support.
>
> One of the hard drives throws some read errors, and that happen to be
> my root drive...
> My system is CentOS 7, and the root partition is a part of LVM.
>
> [root@mgmt ~]# lvscan
> ACTIVE '/dev/centos/root' [<98.83 GiB] inherit
> ACTIVE '/dev/centos/home' [<638.31 GiB] inherit
> ACTIVE '/dev/centos/swap' [<7.52 GiB] inherit
> [root@mgmt ~]#
>
> [root@tftp ~]# file -s /dev/centos/root
> /dev/centos/root: symbolic link to `../dm-3'
> [root@tftp ~]# file -s /dev/centos/home
> /dev/centos/home: symbolic link to `../dm-4'
> [root@tftp ~]# file -s /dev/dm-3
> /dev/dm-3: SGI XFS filesystem data (blksz 4096, inosz 256, v2 dirs)
> [root@tftp ~]# file -s /dev/dm-4
> /dev/dm-4: SGI XFS filesystem data (blksz 4096, inosz 256, v2 dirs)
>
>
> [root@tftp ~]# xfs_repair /dev/centos/root
> Phase 1 - find and verify superblock...
> superblock read failed, offset 53057945600, size 131072, ag 2, rval -1
>
> fatal error -- Input/output error

look at dmesg, see what the kernel says about the read failure.

You might be able to use https://www.gnu.org/software/ddrescue/
to read as many sectors off the device into an image file as possible,
and that image might be enough to work with for recovery. That would be
my first approach:

1) use dd-rescue to create an image file of the device
2) make a copy of that image file
3) run xfs_repair -n on the copy to see what it would do
4) if that looks reasonable run xfs_repair on the copy
5) mount the copy and see what you get

But if your drive simply cannot be read at all, this is not a filesystem
problem, it is a hardware problem. If this is critical data you may wish
to hire a data recovery service.

-Eric

> [root@tftp ~]#
>
>
> smartctl shows some pending sectors on /dev/sda, and no reallocated
> sectors (yet?).
>
> Can someone please give me a hand to bring root partition back to life
> (ideally)? Or, at least, recover a couple of critical configuration
> files...
>
>
> ---
> Best regards,
> Andrey
>