Synology DS418 on v6.2.4-25556 does not allow shrinking of volumes via the GUI. Thus, this must be done via an SSH terminal. This gist is written as generically as possible so that it works for the general use-case of shrinking volumes formatted with the BTRFS filesystem, and then expanding another one. For this scenario, it's a volume that's being used for Time Machine.
- SSH into the Synology NAS and switch to root account with
sudo su
. - Run
btrfs filesystem show
to list the volumes:
root@SynologyNAS:~# btrfs filesystem show