Hi Łukasz
I moved the discussion to
devel@ovirt.org since it is more appropriate for this issue.
After doing a few vm backups, something breaks and I am unable to perform any operations.
I cannot do incremental backups and even full backups doesn't work. I have this issue third time. I don't know how to fix this so I am currently making new vms for testing purposes
VDSM ovirt44-h2.storware.local command StartVmBackupVDS failed: Backup Error: {'vm_id': '116aa6eb-31a1-43db-9b1e-ad6e32fb9260', 'backup': <vdsm.virt.backup.BackupConfig object at 0x7f42602bba20>, 'reason': "Error starting backup: internal error: unable to execute
QEMU command 'transaction': Dirty bitmap 'ef0dfe55-c08c-4d9e-ad32-d6b6d5cbdac6' not found"}
This means that libvirt cannot find the dirty bitmap when starting the backup.
When we start a backup, we get the list of checkpoints from libvirt and we
redefine all checkpoints. We assume that all redefined checkpoints have
a bitmap in qemu at the time of the redefine.
Peter, is this assumption correct?
If libvirt and engine agree on the existing checkpoints, we start the backup.
In this case one of the bitmaps was missing, so the backup failed.
We know about some flows that may cause loss of the bitmaps:
- copying disks (bitmaps are not copied yet)
- live storage migration (it copy the disks)
- deleting snapshots
- live migration may cause this, not tested yet
- unclean shutdown of the vm
- storage is not accessible when vm is terminated
Did you do any of these operations on the tested vm?
Some of the issues can never be fixed, like unclean shutdown or storage
issue when qemu try to write the bitmaps to disk. So your backup application
must be able to recover from this error.
However oVirt does not provide a useful error that enables recovery. We have
a special error when full backup is required, but it seem that this error is
not returned in this case, and instead we return internal error.
Also since you cannot do a full backup after this error, I guess that engine
did not delete the checkpoint with the missing bitmap. This is not surprising
since the error returned from vdsm is a generic error (BackupError), so engine
cannot tell what is the reason for the failure.
Did you check the backup events? What was the backup completion event?
See this example how to get backup events:
Eyal, looking at the API docs:
Event code is an integer. This is not usable for detecting errors since the value
is not part of the API. We need an enum like:
Peter, do we have a specific error code in libvirt about missing bitmap? we need
this to pass useful error to engine, and engine needs this error to pass useful
error to the user.
The error seen here is generated by:
flags = libvirt.VIR_DOMAIN_BACKUP_BEGIN_REUSE_EXTERNAL
try:
dom.backupBegin(backup_xml, checkpoint_xml, flags=flags)
except libvirt.libvirtError as e:
raise exception.BackupError(
reason="Error starting backup: {}".format(e),
vm_id=
vm.id,
backup=backup_cfg)
Looking in the documentation:
There are no specified errors so we cannot detect the reason for the failure
and return meaningful error to our caller.
Peter, how do you suggest to recover from internal errors? how can we
tell if this temporary error that can succeed in the next attempt, or an error
that requires starting from full backup?
Nir