Time machine backup volumes served out by netatalk3 sometimes fail with the following error:
Time Machine couldn't complete the backup to "Titan AFP". The backup disk is not in Mac OS Extended (Journaled) format, which is required. Open Time Machine preferences to select a different backup disk.
To get around this error, netatalk just needs to be restarted and the Time Machine backup started manually from the machine that was attempting to backup.
My setup is FreeBSD 9.1 running netatalk 3.0.1 with five OS X Mountain Lion computers backing up daily to the share at staggered times. Each machine has its own share configured in netatalk. Each backup volume is on its own ZFS file system with refquota and refreservation limits configured. Also, each backup volume is snapshotted daily so that I can revert the backup volume if it gets corrupted (earlier versions of netatalk would corrupt the backups intermittently).
Here is the typical Time Machine backup volume configuration in afp.conf:
[Shade's Backup] path = /tank/timemachine/shade hosts allow = 192.168.0.111 time machine = yes unix priv = yes ;convert appledouble = no