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

Post-it

New Member
Dec 8, 2021
7
0
1
60
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
 

Dunuin

Famous Member
Jun 30, 2020
6,671
1,546
149
Germany
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%.
 
Last edited:

Post-it

New Member
Dec 8, 2021
7
0
1
60
Thanks for your reply, i have enabled discard on the VM. I will check also for the volblocksize and post results after
 

Dunuin

Famous Member
Jun 30, 2020
6,671
1,546
149
Germany
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

New Member
Dec 8, 2021
7
0
1
60
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" ?
 
Last edited:

Post-it

New Member
Dec 8, 2021
7
0
1
60
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 !
 

About

The Proxmox community has been around for many years and offers help and support for Proxmox VE, Proxmox Backup Server, and Proxmox Mail Gateway.
We think our community is one of the best thanks to people like you!

Get your subscription!

The Proxmox team works very hard to make sure you are running the best software and getting stable updates and security enhancements, as well as quick enterprise support. Tens of thousands of happy customers have a Proxmox subscription. Get your own in 60 seconds.

Buy now!