[Qemu-discuss] QCOW2 Image Corrupted - overlaps with active L2 table

[Andrew Martin]

Hello,

I am running QEMU 2.0.0 and libvirt 1.2.2 on Ubuntu 14.04 LTS. My KVM VMs use
QCOW2 files stored in a local ext4 filesystem. This normally works great,
however today I experienced corruption of one of my VMs disks, causing a kernel
panic in the VM: 
qcow2: Preventing invalid write on metadata (overlaps with active L2 table); 
image marked as corrupt.

I cannot correlate this with any errors in dmesg or other logs on the host. The
other VMs on the host are still running fine with no corruption. I was able to
run "qemu-img check -r all <image>" and have it repair the errors:
The following inconsistencies were found and repaired:

    24528 leaked clusters 5 corruptions

While this appears to have fixed it (I can now boot the VM), I'm concerned that
there still may be corrupt data on the disk and I'd like to determine why this
happened. What would cause a qcow2 file to become corrupt? Is there should I can
do to prevent this kind of corruption from happening in the future?

Thanks,

Andrew