Can I gzip VHD images?

I’m using a linux server, and I would like to avoid brtfs or ZFSOnlinux.

Should I be low on free space, can I gzip *.vhd files? (and then change filename in backup_images table to .vhd.gz, so urbackup could still be able to manage/delete the image). Obviously I should gunzip them before restores.

Could it work?

Yes, should be okay, if you don’t base differential image backups on them. Don’t know what will happen if you do. It only needs the .hash file, which it finds by appending .hash to the .vhd name, but the vhd-writer opens, reads and adds the id of the parent .vhd-file to the new .vhd file.