virsh backup-begin problem

[Peter Krempa]

On Wed, Jan 20, 2021 at 20:49:49 +0300, Andrey Fokin wrote:
> Colleagues, could you please advise what a problem could be in XML file in
> case of:
> virsh backup-begin lubuntu2 ./backup.xml
> 
> where backup.xml -
> <domainbackup>
>     <disk name='/var/lib/libvirt/images/lubuntu2.qcow2' type='file'>
>     <target file='$PWD/scratch1.img'/>
>     <driver type='raw'/>
>     </disk>
>     <disk name='/var/lib/libvirt/images/lubuntu2-1.qcow2' type='file'>
>       <target file='$PWD/scratch2.img'/>
>       <driver type='raw'/>
>     </disk>
> </domainbackup>

snip ...

You forgot to add what you are observing, but I presume:

'operation unsupported: incremental backup is not supported yet'

Unfortunately it's what it says on the tin. The implementation of the
incremental backup code is not finished yet, thus the feature is
disabled.

If you want to test-drive incremental backup APIs, you can enable the
experimental feature by using the XML documented in:

https://libvirt.org/drvqemu.html#xmlnsfeatures

to enable a feature named 'incremental-backup'. Please make sure to read
the caveats of doing so thoroughly.

I also advise not to combine incremental backups with snapshots
(virDomainSnapshot* APIs) and blockjobs (virDomainBlock* APIs) as that
will not work properly without a patch enabling also experimental qemu
features.

I also suggest you use the latest qemu for this.