If the server runs out of space for backing up the Mac computers on your network, you can connect another disk to the server and make it the storage location in the Time Machine pane of the Server app.
Users whose Time Machine preferences were set to use the server for backup storage automatically begin using the server’s new backup disk.
After selecting a different backup disk, you should advise users that their first backup will take longer because it’s a full backup. Time Machine service doesn’t copy users’ backup data from the old backup disk to the new one.