I just had the chance to help debugging another case of this, and it turned out that qemu-img snapshot was used on the image while the VM is running. This was likely the root cause of the corruption. So if you're reading this, it's probably already too late, but I want to spell it out anyway:
WARNING: Never open the same disk image from two processes at the same time, except if both are read-only! If your VM is running, use the qemu monitor of that VM (or libvirt functionality, which will do the same internally) to do operations on the image. Use qemu-img only for images of shut down VMs. If you reported in this bug that you are affected, can you please reply and specify whether you ever used qemu-img (except for read-only subcommands) on your image while the VM was running? -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1354167 Title: On VM restart: Could not open 'poppy.qcow2': Could not read snapshots: File too large Status in QEMU: New Bug description: I'm unable to restart a VM. virt-manager is giving me: Error starting domain: internal error: process exited while connecting to monitor: qemu-system-x86_64: -drive file=/var/lib/libvirt/images/poppy.qcow2,if=none,id=drive-virtio- disk0,format=qcow2: could not open disk image /var/lib/libvirt/images/poppy.qcow2: Could not read snapshots: File too large From the command line trying to check the image also gives me: qemu-img check poppy.qcow2 qemu-img: Could not open 'poppy.qcow2': Could not read snapshots: File too large This bug appears with both the default install of qemu for ubuntu 14.04: qemu-img version 2.0.0, Copyright (c) 2004-2008 Fabrice Bellard And the latest version. qemu-img version 2.1.50, Copyright (c) 2004-2008 Fabrice Bellard Host: Dual E5-2650 v2 @ 2.60GHz 32GB Memory 4TB Disk space (2.1TB Free) Host OS: Ubuntu 14.04.1 LTS 64bit Guest: Ubuntu 14.04 64bit Storage Size: 500gb To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1354167/+subscriptions