Read-only VM with stdout


New Member
Apr 10, 2022

I backup some VMs using SSH with vzdump redirecting to stdout, similar to the command below:
ssh root@pve-server vzdump 100 --mode snapshot $VZDUMP_PARAMETERS --stdout > ${SERVER}_${NAME}_$(date +%Y-%m-%d).vma 2> >(tee -a ${SERVER}_${NAME}_$(date +%Y-%m-%d).log >&2)

But I noticed that if the connection goes offline, the machine being dumped starts to show erros and becomes read-only system.

Is it possible to prevent this from happening?



  • pveversion.txt
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This is because backup is implemented as a shim for write activity. During the backup if client/VM tries to write to disk and that block has not been backed up yet (based on dirty bitmap), PVE will try to backup that block out of order to get a consistent backup view.
In essence, backup connection is in critical path of a write. With IO blocked on write the OS/Kernel will wait for a bit and after a timeout convert the disk to RO as a precaution.
The only short term solution is to have a rock solid backup server and connectivity to it. The ideal solution would be to offload saving the blocks to snapshots on the backend storage.

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