Comment 100 for bug 1470250

Actually I got this on 3 VMs on my Azure Pack. One 15.10 and two 14.04.03.
On 15.10 I tried to fsck the root fs before reboot. What could go wrong as fs is already read-only I thought.
Here is the session:

~# touch /oioi
touch: cannot touch '/oioi': Read-only file system
~# fsck / <--- At this point it corrupted everything already.
fsck from util-linux 2.26.2
e2fsck 1.42.12 (29-Aug-2014)
cloudimg-rootfs: recovering journal
fsck.ext4: Bad magic number in super-block while trying to re-open cloudimg-rootfs

cloudimg-rootfs: ********** WARNING: Filesystem still has errors **********

~# fsck -f /
fsck from util-linux 2.26.2
fsck.ext4: Unable to resolve 'UUID=5370f2f3-e06a-4682-bc53-2f844792ebe1'
~# ls -la /
total 0

After reboot grub said it cannot find FS so I booted it from another HDD and fcsked from that. It reported a lot of errors but rendered the FS as explained before - everything in lost+found.

On 14.04 I rebooted without fsck. After boot it said that FS i corrupted so I can Skip mounting it (what root?) or try Manualy fix it. So I pressed the M but it looked like it's frozen.

Luckily I restored all VMs from the backup. Yes, the very same backup that actually triggered the issue as we found it's 100% correlated that the corruption happens when the backup job starts on HV.