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

[Roger Willcocks]

On Tue, 2012-01-24 at 11:13 +0100, Christian Kildau wrote:
> Top posting... sorry.
> 
> I have now found dozens of other users with a similar issue! e.g.
> http://www.linuxquestions.org/questions/linux-general-1/cannot-mount-hard-disk-block-count-exceeds-size-of-device-bad-partition-table-880149/
> 
> To make it short all of these users were running ext4 and a fs resize to the new geometry fixed their problems! Sadly XFS doesn't support shrinking the fs(?).
> 

It seems fairly clear that your drive or the bios is lying about its
capacity. The filesystem occupies the entire disk, but the disk has
become 'smaller'. A quick web search suggests a 'hidden protected area'
- the two block counts in this link line up with the before and after
sizes you're seeing:

http://lime-technology.com/forum/index.php?topic=13440.0;wap2

It would be instructive to see what 'hdparm -N /dev/sdd' says on your
system. And a dmesg log would be handy too.

Note that this is /not/ a problem with xfs. The right fix is to tell the
drive to report its actual capacity, not to shrink the filesystem.