[SOLVED] Huge backup size when backup but small used disk on VM

[Post-it]

Hello

I have a simple problem : i have a Windows server 2019 on a VM.
Space used on the disk of the VM : 179Go
Size of the VM disk : 1.65To

When i backup the VM with proxmox, my backup size is 919Go. Why ?
I cannot defrag the disk on the VM

For information, I use a zpool storage for the disk of the VM
The storage destination for the backup is a NFS Nas.

Thank you for your help

 

[czechsys]

Check discard/trim functions.

 

[Dunuin]

And beside not working discard/trim the padding overhead of a raidz1/2/3 could also increase the size when using a too low volblocksize. But paddin overhead alone shouldn't be more than 200%.

 

[Post-it]

Thanks for your reply, i have enabled discard on the VM. I will check also for the volblocksize and post results after

 

[Dunuin]

Thanks for your reply, i have enabled discard on the VM. I will check also for the volblocksize and post results after

Make sure to enable discard/TRIM in the guest OS, that the "discard"checkbox at the virtual disk in the VMs hardware tab is enabled and that you use a virtul disk controller like virtio SCSI with a protocal like SCSI that acually also supports TRIM commands. IDE or virtioblk for example won't allow that.

 

[Post-it]

Make sure to enable discard/TRIM in the guest OS, that the "discard"checkbox at the virtual disk in the VMs hardware tab is enabled and that you use a virtul disk controller like virtio SCSI with a protocal like SCSI that acually also supports TRIM commands. IDE or virtioblk for example won't allow that.

Yes all required components were installed before applying discard on VM. I also checked that Trim was activated in guest OS with "fsutil behavior set DisableDeleteNotify" with result 0 (enabled) Enabling trim function in windows.

So, results are : when i backup my VM, the size of my backup is now at 731Go, which is better. But it is not the expected result.
Do i need to reduce the size of my partition in the guest os and then rollback to my initial size of partition to force windows to say to proxmox "Hey ! Here are data that you could use to rewrite" ?

 

[Post-it]

Finally, after waiting few days without having done anything, backup size now are at 146Go which is now Ok in agreement with data used on guest host. Problem now solved. Thanks !