How to shrink VM disk

[Benoît Fontaine]

Hi,
I have a proxmox with 3 containers and 2 virtual machines, all on a ZFS storage. There is one thing that is automatic with containers and that I would like to do with VMs:

I create a virtual machine with a 500 GB disk. On the ZFS, I enabled the "Thin Provisioning" function, which means that at the beginning, the disk has a size almost zero and grows as and when as I put things on it. Currently, the actual size is around 400 GB.

Then, I delete the files from the virtual machine (from the perspective of the virtual machine, there is only 100 GB of used) and I wish the disk is reduced to save space.

Possible? How?

 

[mbaldini]

You should use virtio-scsi driver with discard option and inside the VM use the TRIM function (fstrim from linux, during the maintenance time in windows)

 

[Benoît Fontaine]

Thanks for your answer.
The disk is SATA, is there a way to change into scsi ?

 

[mbaldini]

Windows or Linux VM ?

 

[Benoît Fontaine]

Windows

 

[mbaldini]

First you should install virtio-scsi drivers, adding a new virtio-scsi virtual disk and installing the driver.
After that you can remove all the virtual disks and re-add them as virtio-scsi with the discard option enabled.
From Windows 7 / Windows server 2008R1 up to Windows 10/Windows Server 2016, TRIM is enabled by default on SSD and thin provisoned disks

 

[Benoît Fontaine]

To remove and re-add, I need to previously clone disks ?
(zfs clone something...).

 

[mbaldini]

From the web interface, in the Hardware tab of the VM, you have the option to DETACH a virtual disk. After you click on detach, the disk is kept as unused, just double click the unused disk and add it as virtio-scsi with discard enabled

 

[Benoît Fontaine]

Ok, thanks !