Warning - Avoid the pain - Don't grow your QCOW2 file beyond 2TB

[IUA2008]

Something we learnt the hard way and I hope others will avoid this "feature" (advised by support) of Proxmox VE.

We were running KVM instance on qcow2 file, and utilised the Resize-Disk option to increase space. Unfortunately this option allows increase in size just above 2Tb on the default ext3 filesystem.

End result, corruption will occur at some point in the future as the disk is written, you just won't know when and it's not recoverable, nor can you restore from vzdump backup.

Hopefully you will have read this before you expand the hard disk volume and avoided this situation. Better still perhaps Proxmox will realise this actually is a design bug in their software and stop growth beyond limits on the supported filesystems.

Thanks and good luck if you're in the same situation.

 

[dietmar]

Next version will use ext4 by default, so this problem will be solved that way (With proxmox installer you can already choose to use ext4).

 

[dietmar]

I also want to mention that real space consumption of qcow2 is non-trivial and impossible to know in advance (snapshots, ...). So it is
not really possible to cleanly fix that on our side. The only real fix is to remove the 2TB limit (use ext4).