Problem with ZSTD compressed backup

michal

Hi,

I am trying to do a backup of relatively large VM (~1TB) with ZSTD compression, it shows that backup is successful and there is no errors in XOA log files:

 Snapshot 
Start: Nov 3, 2020, 03:12:05 PM
End: Nov 3, 2020, 03:12:11 PM
 local_storage 
 transfer 
Start: Nov 3, 2020, 03:12:11 PM
End: Nov 3, 2020, 04:27:34 PM
Duration: an hour
Size: 103.3 GiB
Speed: 23.39 MiB/s
Start: Nov 3, 2020, 03:12:11 PM
End: Nov 3, 2020, 04:27:34 PM
Duration: an hour
Start: Nov 3, 2020, 03:12:05 PM
End: Nov 3, 2020, 04:38:47 PM
Duration: an hour

but when I am trying to restore it, it fails:

IMPORT_ERROR_PREMATURE_EOF()
This is a XenServer/XCP-ng error

The same backup without compression works fine, and it takes 10x more space.
I use XCP-NG 8.1 and xo-server 5.70.0, xo-web 5.74.0.

It looks like some issue of XAPI with VM export/compression. Has anyone run into a similar issue?

olivierlambert

I'm not aware of such problems. Have you tried to import with xe CLI directly to rule out anything with XO?

michal

Export of VM snapshot directly with xe works fine. The output file size was ~700GB.
I used the following commands:

# xe template-param-set is-a-template=false uuid=snapshoot_UUID
# xe vm-export filename=filename.xva vm=snapshoot_UUID compress=zstd
Export succeeded

olivierlambert

I asked for the import

michal

Manual import of the backup does not work, it finishes with the same error.

# xe vm-import (...)
The VM could not be imported; the end of the file was reached prematurely.

olivierlambert

Then I bet on a partial backup, but in any case it shouldn't have been successful.

We are doing a major overhaul on the backup code. But keep us posted if it happens again so we can find a way to reproduce the problem.

michal

So far, I noticed this problem for three VMs. Each time I am trying to perform a backup with zstd compression through XO, the backup is marked as successful, but output XVA file is damaged (incomplete). The backup works fine for all other VMs, and I cannot pinpoint what is special about these faulty VMs.