# \[SOLVED\] Ceph - Can't read/write after a live disk snapshot **URL:** \ **Category:** Product Support\ **Created:** [December 19, 2015, 8:54pm UTC](https://forum.opennebula.io/t/solved-ceph-cant-read-write-after-a-live-disk-snapshot/1618 "2015-12-19T20:54:03Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![michaudg](https://avatars.discourse-cdn.com/v4/letter/m/e9a140/32.png) [@michaudg](https://forum.opennebula.io/u/michaudg)\ **Post date:** [December 19, 2015, 8:54pm UTC](https://forum.opennebula.io/t/solved-ceph-cant-read-write-after-a-live-disk-snapshot/1618/1 "2015-12-19T20:54:03Z")
I successfully made a live disk snapshot on a running Linux VM with qemu-guest-agent installed : Sat Dec 19 15:51:37 2015 [Z0][VM][I]: New LCM state is RUNNING Sat Dec 19 15:51:56 2015 [Z0][VM][I]: New state is ACTIVE Sat Dec 19 15:51:56 2015 [Z0][VM][I]: New LCM state is DISK\_SNAPSHOT Sat Dec 19 15:51:57 2015 [Z0][VMM][I]: Successfully execute transfer manager driver operation: tm\_snap\_create\_live. Sat Dec 19 15:51:57 2015 [Z0][VMM][I]: VM disk snapshot successfully created. Sat Dec 19 15:51:57 2015 [Z0][VM][I]: New LCM state is RUNNING Sat Dec 19 15:51:57 2015 [Z0][LCM][I]: VM disk snapshot operation completed. But after the snapshot, if I try to reboot the system using the reboot command in the guest system, my SSH session closes but the system won’t reboot and never comes back online. If I don’t try to reboot the system and just try to access the disk (read or write, ls, cat, touch, …), my session freezes. I don’t have this problem if I STOP or SUSPEND the VM before doing the disk snapshot. Is the live disk snapshot with Ceph backend is possible? Thank you. ONE 4.14.2 with Ceph 0.94.5 ---
**Author:** ![ruben](https://yyz1.discourse-cdn.com/flex031/user_avatar/forum.opennebula.io/ruben/32/19_2.png) [@ruben](https://forum.opennebula.io/u/ruben)\ **Post date:** [December 19, 2015, 9:18pm UTC](https://forum.opennebula.io/t/solved-ceph-cant-read-write-after-a-live-disk-snapshot/1618/2 "2015-12-19T21:18:40Z")
Yes it is supported, note that if you do not revert the operation is just a rbd snapshot operation on the disk, that should not alter the status of the disk image … A couple of things to check: 1.- If you updated from a previous version, perform a onehost sync 2.- Maybe you can try to install qemu-guest-agent, the driver is actually trying a do a domfsfreeze. Cheers ---
**Author:** ![michaudg](https://avatars.discourse-cdn.com/v4/letter/m/e9a140/32.png) [@michaudg](https://forum.opennebula.io/u/michaudg)\ **Post date:** [December 19, 2015, 9:45pm UTC](https://forum.opennebula.io/t/solved-ceph-cant-read-write-after-a-live-disk-snapshot/1618/3 "2015-12-19T21:45:03Z")
Thanks for your quick help. The qemu-guest-agent is already installed and running. The hosts are also synced. Note that I’m trying to snapshot the system disk (vda, ID-0). Maybe the Ceph live disk snapshot is only possible on non-system target disk? ---
**Author:** ![michaudg](https://avatars.discourse-cdn.com/v4/letter/m/e9a140/32.png) [@michaudg](https://forum.opennebula.io/u/michaudg)\ **Post date:** [December 19, 2015, 11:38pm UTC](https://forum.opennebula.io/t/solved-ceph-cant-read-write-after-a-live-disk-snapshot/1618/4 "2015-12-19T23:38:34Z")
I solved this problem by setting **Cache=writethrough** for the storage disk 0 (system disk). I can now live snapshot the disk without freezing the system. Even with the qemu-guest-agent running, the system freezed after a disk snapshot if the disk Cache option is left blank. …as explained in [the doc](http://docs.opennebula.org/4.14/user/virtual_resource_management/vm_guide_2.html#id1) : Warning Depending on the CACHE the live snapshot may or may not work correctly. For more security use CACHE=writethrough although this delivers the slowest performance. ---
**Author:** ![ruben](https://yyz1.discourse-cdn.com/flex031/user_avatar/forum.opennebula.io/ruben/32/19_2.png) [@ruben](https://forum.opennebula.io/u/ruben)\ **Post date:** [December 22, 2015, 9:08am UTC](https://forum.opennebula.io/t/solved-ceph-cant-read-write-after-a-live-disk-snapshot/1618/5 "2015-12-22T09:08:30Z")
Thanks for letting us know!