Re: How to fix bad superblock or xfs_repair: error - read only 0 of 512 bytes

[Eric Sandeen <sandeen@sandeen.net>]

On Dec 28, 2019, at 3:11 AM, Utpal Bora <cs14mtech11017@iith.ac.in> wrote:
> 
> Hi,
> 
> My XFS home drive is corrupt after trying to extend it with lvm.
> This is what I did to extend the partition.
> 1. Extend Volume group to use a new physical volume of around 1.2TB.
> This was successful without any error.
>    vgextend vg-1 /dev/sdc1
> 
> 2. Extend logical volume (home-lv) to use the free space.
>    lvextend -l 100%FREE /dev/mapper/vg--1-home--lv -r
> 
This probably invoked xfs_growfs

> 3. Resized home-lv and reduce 55 GB
>   lvreduce -L 55G  /dev/mapper/vg--1-home--lv -r
> 
XFS cannot shrink.  This corrupted your filesystem by truncating the block device.

> I assumed that -r will invoke xfs_grow internally.
> Everything was working fine until the server was restarted.
> After restart, the home volume is not mounting. Please see the following.
> 
> server% sudo mount -t xfs /dev/mapper/vg--1-home--lv /home
> mount: /home: can't read superblock on /dev/mapper/vg--1-home--lv.
> 
> server% dmesg| tail
> [162580.208796] attempt to access beyond end of device
> [162580.208800] dm-3: rw=4096, want=6650552320, limit=6640066560
> [162580.208805] XFS (dm-3): last sector read failed

Because you chopped off 55g from the end.

> server% sudo xfs_repair -n

Repair cannot read blocks that have been removed from the filesystem.


> /dev/mapper/vg--1-home--lv
> Phase 1 - find and verify superblock...
> xfs_repair: error - read only 0 of 512 bytes

Failed to read a backup super beyond the end of the reduced lv.

Grow the lv back to 100% I.e. the size before the lvreduce and it’ll probably be ok again

-Eric

> OS: Ubuntu Server 18.04.3
> Kernel: 4.15.0-72-generic
> 
> I have gone through the earlier posts on this subject. They did not help me.
> 
> Is it possible to repair the XFS volume? Kindly suggest.
> 
> Regards,
> 
> Utpal Bora
> Ph.D. Scholar
> Computer Science & Engineering
> IIT Hyderabad
>