We have played a bit around with external snapshots (as suggested by Eric Blake in post #3), however, it appears that external snapshots are not fully supported yet. While I can create external snapshots, I'm unable to revert to them using virt-manager (which we use for managing our VM farm):
Error running snapshot 'test': unsupported configuration: revert to external snapshot not supported yet Traceback (most recent call last): File "/usr/share/virt-manager/virtManager/asyncjob.py", line 89, in cb_wrapper callback(asyncjob, *args, **kwargs) File "/usr/share/virt-manager/virtManager/asyncjob.py", line 125, in tmpcb callback(*args, **kwargs) File "/usr/share/virt-manager/virtManager/libvirtobject.py", line 82, in newfn ret = fn(self, *args, **kwargs) File "/usr/share/virt-manager/virtManager/domain.py", line 1225, in revert_to_snapshot self._backend.revertToSnapshot(snap.get_backend()) File "/usr/lib/python2.7/dist-packages/libvirt.py", line 1945, in revertToSnapshot if ret == -1: raise libvirtError ('virDomainRevertToSnapshot() failed', dom=self) libvirtError: unsupported configuration: revert to external snapshot not supported yet .... which means that using external snapshots is not an option for us. Kevin Wolf, over which time period did you run the VMs? Have you made any kind of i/o intensive stuff in the guest itself? e.g. user logon / logoff, serving the web, installing updates We continue to have big problems with the described issue, here's another example (23GB Vs. 41GB on disk): # ls -lah -rw-r--r-- 1 root root 41G Jan 18 10:57 W10-ROUTER-0.img # qemu-img info W10-ROUTER-0.img image: W10-ROUTER-0.img file format: qcow2 virtual size: 320G (343597383680 bytes) disk size: 23G cluster_size: 65536 backing file: /var/lib/libvirt/images/W10-MASTER-IMG.qcow2 Snapshot list: ID TAG VM SIZE DATE VM CLOCK 1 1 6.0G 2019-01-04 14:51:49 01:09:32.118 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1810603 Title: QEMU QCow Images grow dramatically Status in QEMU: New Bug description: I've recently migrated our VM infrastructure (~200 guest on 15 hosts) from vbox to Qemu (using KVM / libvirt). We have a master image (QEMU QCow v3) from which we spawn multiple instances (linked clones). All guests are being revert once per hour for security reasons. About 2 weeks after we successfully migrated to Qemu, we noticed that almost all disks went full across all 15 hosts. Our investigation showed that the initial qcow disk images blow up from a few gigabytes to 100GB and more. This should not happen, as we revert all VMs back to the initial snapshot once per hour and hence all changes that have been made to disks must be reverted too. We did an addition test with 24 hour time frame with which we could reproduce this bug as documented below. Initial disk image size (created on Jan 04): -rw-r--r-- 1 root root 7.1G Jan 4 15:59 W10-TS01-0.img -rw-r--r-- 1 root root 7.3G Jan 4 15:59 W10-TS02-0.img -rw-r--r-- 1 root root 7.4G Jan 4 15:59 W10-TS03-0.img -rw-r--r-- 1 root root 8.3G Jan 4 16:02 W10-CLIENT01-0.img -rw-r--r-- 1 root root 8.6G Jan 4 16:05 W10-CLIENT02-0.img -rw-r--r-- 1 root root 8.0G Jan 4 16:05 W10-CLIENT03-0.img -rw-r--r-- 1 root root 8.3G Jan 4 16:08 W10-CLIENT04-0.img -rw-r--r-- 1 root root 8.1G Jan 4 16:12 W10-CLIENT05-0.img -rw-r--r-- 1 root root 8.0G Jan 4 16:12 W10-CLIENT06-0.img -rw-r--r-- 1 root root 8.1G Jan 4 16:16 W10-CLIENT07-0.img -rw-r--r-- 1 root root 7.6G Jan 4 16:16 W10-CLIENT08-0.img -rw-r--r-- 1 root root 7.6G Jan 4 16:19 W10-CLIENT09-0.img -rw-r--r-- 1 root root 7.5G Jan 4 16:21 W10-ROUTER-0.img -rw-r--r-- 1 root root 18G Jan 4 16:25 W10-MASTER-IMG.qcow2 Disk image size after 24 hours (printed on Jan 05): -rw-r--r-- 1 root root 13G Jan 5 15:07 W10-TS01-0.img -rw-r--r-- 1 root root 8.9G Jan 5 14:20 W10-TS02-0.img -rw-r--r-- 1 root root 9.0G Jan 5 15:07 W10-TS03-0.img -rw-r--r-- 1 root root 10G Jan 5 15:08 W10-CLIENT01-0.img -rw-r--r-- 1 root root 11G Jan 5 15:08 W10-CLIENT02-0.img -rw-r--r-- 1 root root 11G Jan 5 15:08 W10-CLIENT03-0.img -rw-r--r-- 1 root root 11G Jan 5 15:08 W10-CLIENT04-0.img -rw-r--r-- 1 root root 19G Jan 5 15:07 W10-CLIENT05-0.img -rw-r--r-- 1 root root 14G Jan 5 15:08 W10-CLIENT06-0.img -rw-r--r-- 1 root root 9.7G Jan 5 15:07 W10-CLIENT07-0.img -rw-r--r-- 1 root root 35G Jan 5 15:08 W10-CLIENT08-0.img -rw-r--r-- 1 root root 9.2G Jan 5 15:07 W10-CLIENT09-0.img -rw-r--r-- 1 root root 41G Jan 5 15:08 W10-ROUTER-0.img -rw-r--r-- 1 root root 18G Jan 4 16:25 W10-MASTER-IMG.qcow2 You can reproduce this bug as follow: 1) create an initial disk image 2) create a linked clone 3) create a snapshot of the linked clone 4) revert the snapshot every X minutes / hours Due the described behavior / bug, our VM farm is completely down at the moment (as we run out of disk space on all host systems). A quick fix for this bug would be much appreciated. Host OS: Ubuntu 18.04.01 LTS Kernel: 4.15.0-43-generic Qemu: 3.1.0 libvirt: 4.10.0 Guest OS: Windows 10 64bit To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1810603/+subscriptions