Apple Time Machine backups failing: "the backup on rockstor is already in use"

Yesterday I created a new share and enabled time machine backups, and then set up my macbook to back up to it. It seems to have completed a full backup, or at least most of one, but I keep getting these notifications that say:

Backup Failed
The backup on “rockstor” is already in use.

And then if I hit more details I get:

Time Machine couldn’t complete the backup to “rockstor”.
The backup disk image "/Volumes/apple_time_machine_backups on Rockstor/Nathan’s Macbook Pro.sparsebundle is already in use.
Latest successful backup: Yesterday, 8:38 PM

This seems to be happening about once an hour. There are two macbooks in the house, but mine is the only one that’s set to backup to my Rockstor server.

I’ve read about this occurring with other NAS systems and that the solution is to disconnect the user in the NAS’s UI… but I don’t know how to do that with Rockstor (?)


I noticed that this seems to happen when I already have a (different) share from the rockstor server mounted locally on my macbook. I’m using the same credentials for both the backup and for regular file browsing. Once I click the “eject” icon in finder, the next backup succeeds. I’m going to experiment with a few things, such as a separate account for backups, or connecting via smb instead of afp and see if I can get it to stop whining.

@nfriedly try to disable and then re-enable the afp service.
This used to solve the problem for me.


I rebooted the server which more or less fixed it (after I found a monitor & keyboard, rebooted again, and selected the correct option in grub… but that’s another story).

I think the error popped up once since then, but it may have been something else because it went away on it’s own.