Backup size equal to disk size

[xFede46]

Hello everyone,

i'm trying to backup two vm to an external usb device (nvme 2tb), guest os is win srv 2022 (vm1 600gb and vm2 200gb) with guest agent installed.
The VMs has their disks on a zfs partition made on 4 samsung ssd in raid10, with thin provision enabled.
The SCSI Controller is VirtIO SCSI, the disk type is scsi, the discard is on, the ssd emulation is on.
On the guest OS the trim is enabled and i also run optimize-disk.
On PVE i checked lvm.conf and issue_discards is set to 1, fstrim and fstrim timer are enabled and running.

If i backup the two VMs to the external disk it backup 600gb for vm1 and 200gb for vm2, if i go in the zfs tab i read "963gb free | 33gb allocated".
I searched for a whole day and i can't understand why it is doing backup as big as the vm disk.

PS: the same behavior is obtained doing backup on an internal disk
PS2: the snapshot of the vm can be taken in a few seconds with correct sizes (30gb for each vm), only the backup done from the backup tab is "broken"
Thanks in advice

 

[LnxBil]

Trim does not mean that it works all the time. I overwrite the free space in the VM with zeros, which yields a smaller disk more often than just having everything TRIM enabled. For Unix, a simple dd command will work, for Windows, there is a sysinternals tool.