When using an encrypted drive in a virtual machine, the VM image starts very small if you do not initialize the drive with random data. When you fill the drive, it grows, but when you delete files it doesn't shrink.
With a not encrypted drive, you can fill the drive with zeros (i.e. by creating a large file filled with zeros), so the VM-Software can compress it. But with a encrypted drive, the zeros get encrypted and the VM image cannot shrink.
Is there some kind of TRIM command like SSDs have, which zeros out the unused space of a filesystem on the underlying encrypted blockdevice?