Traditional (no LVM) disk setup means space does not get recouped from deletion of files from VMS

[fosslinux]

Qubes OS version:

R4.0

Affected component(s):

any VM's

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Steps to reproduce the behavior:

1. Setup Qubes without LVM or LVM-thin, just normal disk setup.
2. Make a big file in a VM (eg dd if=/dev/zero of=bigfile.img bs=1000000 count=10000)
3. Reboot the VM and ensure that the disk space has updated in Qubes Manager to show that the big file exists.
4. Delete the file.
5. Check the size in Qubes Manager.

Expected behavior:

The size of the VM should be (sizeWithBigFile - sizeOfBigFile).

Actual behavior:

The file gets deleted but remains in the disk space of the VM.

General notes:

In Qubes R3.2 the file would get deleted upon an fstrim operation in the VM. Now, in Qubes 4.0, due to the use of LVM Thin by default, fstrim is no longer needed to make the VM usage smaller. If LVM thin is not used, then the VM will not get smaller. This is visible by running du on the VM image.

fstrim does not work either, see #3255 for more details.

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Related issues:

#3255