Deleted qube's data space still not free

[apparatus]

I guess you need to enable discard for LVM for it to free up the space after volume deletion:

If you are using Qubes with LVM, you may also want to set issue_discards = 1 in /etc/lvm/lvm.conf. Setting this option will permit LVM to issue discards to the SSD when logical volumes are shrunk or deleted. In R4.x, LVM Logical volumes are frequently deleted (every time a disposable VM is shut down, for example) so you may want to set issue_discards = 1 if using an SSD, but see the article linked in the first section of this page. However, this is relatively rare in R3.x.

Disk Trimming

Disk trimming is the procedure by which the operating system informs the underlying storage device of which storage blocks are no longer in use. It does this by issuing an ATA_TRIM command for the block. This is also known as a discard. In this way, the storage device can perform garbage collection of the unused blocks and internally prepare them for reuse. SSDs in general benefit from this, while HDDs do not. In a Linux system running on bare metal, this is relatively straight-forward. When in…