Hello,

I am sending logs from vdsm, maybe they will help. I cannot find useful libvirt logs and file libvirt.log doesn't exists.

Best Regards,

Łukasz Kołaciński

Junior Java Developer

e-mail: l.kolacinski@storware.eu

 

ul. Leszno 8/44 01-192 Warszawa www.storware.eu

 

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---

Od: Nir Soffer <nsoffer@redhat.com>
Wysłane: środa, 29 lipca 2020 00:31
Do: Łukasz Kołaciński <l.kolacinski@storware.eu>
DW: Eyal Shenitzky <eshenitz@redhat.com>; Mateusz Maziarz <m.maziarz@storware.eu>; Marcin Kubacki <m.kubacki@storware.eu>; Peter Krempa <pkrempa@redhat.com>; devel <devel@ovirt.org>
Temat: Re: Issue with ovirt 4.4 after doing some incremental backups.

 

On Tue, Jul 28, 2020 at 4:05 PM Łukasz Kołaciński <l.kolacinski@storware.eu> wrote:

Hello,

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:

https://github.com/oVirt/ovirt-engine-sdk/blob/4a143351fcd3cdb0df8c50888931655e8226d7a4/sdk/examples/backup_vm.py#L345

https://github.com/oVirt/ovirt-engine-sdk/blob/4a143351fcd3cdb0df8c50888931655e8226d7a4/sdk/examples/backup_vm.py#L461

Eyal, looking at the API docs:

http://ovirt.github.io/ovirt-engine-api-model/master/#types/event

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:

http://ovirt.github.io/ovirt-engine-api-model/4.4/#types/image_transfer_phase

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:

https://libvirt.org/html/libvirt-libvirt-domain.html#virDomainBackupBegin

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