On Fri, Jan 14, 2022 at 23:39:10 +0600, Ahmad Ismail wrote:
> Normally when I backup a kvm machine I shutdown the machine then run:

[...]

> The problem with this help is, it is not clear enough.
>
> I understand that I should use virsh backup-begin vm1 to backup a live kvm
> machine. However, this command only create .qcow2 files. What about the .xml
> file.
>
> What does --backupxml , --checkpointxml & --reuse-external actually do?
>
> When should I use them?

'man virsh' states:

   backup-begin
       Syntax:

          backup-begin domain [backupxml] [checkpointxml] [--reuse-external]

       Begin a new backup job. If backupxml is omitted, this defaults  to
       a  full  backup  using a push model to filenames generated by lib‐
       virt; supplying XML allows fine-tuning such as requesting  an  in‐
       cremental  backup  relative  to an earlier checkpoint, controlling
       which disks participate or which filenames are  involved,  or  re‐
       questing  the use of a pull model backup.  The backup-dumpxml com‐
       mand shows any resulting values assigned by libvirt. For more  in‐
       formation           on          backup          XML,          see:
       https://libvirt.org/formatbackup.html

       If --reuse-external is used it instructs libvirt to  reuse  tempo‐
       rary and output files provided by the user in backupxml.

       If checkpointxml is specified, a second file with a top-level ele‐
       ment of domaincheckpoint is used to create a  simultaneous  check‐
       point,  for  doing a later incremental backup relative to the time
       the backup was created. See checkpoint-create for more details  on
       checkpoints.

       This  command returns as soon as possible, and the backup job runs
       in the background; the progress of a  push  model  backup  can  be
       checked with domjobinfo or by waiting for an event with event (the
       progress of a pull model backup is under the control  of  whatever
       third  party  connects  to  the NBD export). The job is ended with
       domjobabort.


Does this clarify it sufficiently?