I know this post is old but this has recently cropped up for me. I have been backing up with Time Machine for months without a single alert. It started happening after I replaced the failed battery on my RAID card. A coincidence...however the prolonged down time surely caused an SMC (and perhaps PRAM) reset which I assume triggered the change in behavior.
I've pinned it down to Time Machine backing up service settings, in particular the Open Directory archive. Time Machine backs up all the service data independently from the rest of the data on your server startup volume.
http://support.apple.com/kb/ht5139
You can see this data in Terminal.
serveradmin$ cd /Volumes/[YourBackupVolume]/Backups.backupdb/[YourServerName]/Latest/[YourBootVolume]/.ServerBackups
serveradmin$ ls -al
total 16
drwxr-xr-x@ 2 root admin 68 4 Jun 14:44 (null)
drwxr-xr-x@ 14 root admin 476 4 Jun 14:44 .
drwxrwxr-t@ 43 root admin 1462 4 Jun 14:43 ..
-rw-r--r--@ 1 root admin 37 4 Jun 14:44 .serverBackupSignature
drwxr-xr-x@ 2 root admin 68 4 Jun 14:44 addressBookServer
drwxr-xr-x@ 2 root admin 68 4 Jun 14:44 calendarServer
drwxr-xr-x@ 5 root admin 170 4 Jun 14:44 iChatServer
drwxr-xr-x@ 6 root admin 204 4 Jun 14:44 mailServer
-rw-r--r--@ 1 root admin 3826 4 Jun 14:44 master.browse.plist
drwxr-xr-x@ 4 root admin 136 4 Jun 14:43 openDirectory
drwxr-xr-x@ 61 root admin 2074 4 Jun 14:44 serverSettings
drwxr-xr-x@ 23 root admin 782 4 Jun 14:44 sharePoints
drwxr-xr-x@ 8 root admin 272 4 Jun 14:44 webServer
drwxr-xr-x@ 2 root admin 68 4 Jun 14:44 wikiServer
If you take a look inside the openDirectory folder you should see this:
serveradmin$ cd openDirectory
serveradmin$ ls -al
total 81936
drwxr-xr-x@ 4 root admin 136 4 Jun 15:32 .
drwxr-xr-x@ 14 root admin 476 4 Jun 15:33 ..
-rw-rw----@ 1 root admin 41947136 4 Jun 15:32 ServerBackup_OpenDirectoryMaster.sparseimage
-rw-r--r--@ 1 root admin 249 4 Jun 15:32 openDirectory.browse.plist
The ServerBackup_OpenDirectoryMaster.sparseimage contains an archive of your Open Directory database like the one you create from Server Admin. The only difference is that it appears to be unencrypted. This is a bit worrying since Snow Leopard, as far as I know, does not have an option to encrypt your Time Machine backup. This image seems to invisibly mount whenever a Time Machine backup is triggered. This can be verified by checking /private/var/log/system.log and filtering for backup
serveradmin$ tail -b 100 /var/log/system.log | grep backup
Jun 4 16:00:56 yourservername com.apple.backupd[25117]: Starting standard backup
Jun 4 16:00:56 yourservername com.apple.backupd[25117]: Backing up to: /Volumes/YourBackupVolume/Backups.backupdb
Jun 4 16:00:56 yourservername servermgrd[75]: servermgr_backup: TimeMachinePreBackupHook called.
Jun 4 16:09:26 yourservername servermgrd[75]: servermgr_backup: TimeMachinePreBackupHook done.
Jun 4 16:09:44 yourservername com.apple.backupd[25117]: No pre-backup thinning needed: 4.60 GB requested (including padding), 8.40 GB available
Jun 4 16:10:14 yourservername com.apple.backupd[25117]: Copied 744 files (364.4 MB) from volume YourBootDrive.
Jun 4 16:10:14 yourservername com.apple.backupd[25117]: No pre-backup thinning needed: 4.09 GB requested (including padding), 8.04 GB available
Jun 4 16:10:17 yourservername com.apple.backupd[25117]: Copied 87 files (877 KB) from volume YourBootDrive.
Jun 4 16:10:18 yourservername servermgrd[75]: servermgr_backup: TimeMachinePostBackupHook called.
Jun 4 16:10:18 yourservername servermgrd[75]: servermgr_backup: TimeMachinePostBackupHook done.
Jun 4 16:10:18 yourservername com.apple.backupd[25117]: Starting post-backup thinning
Jun 4 16:10:29 yourservername com.apple.backupd[25117]: Deleted backup /Volumes/YourBackupVolume/Backups.backupdb/yourservername/2013-06-03-155910: 8.40 GB now available
Jun 4 16:10:29 yourservername com.apple.backupd[25117]: Post-back up thinning complete: 1 expired backups removed
Jun 4 16:10:29 yourservername com.apple.backupd[25117]: Backup completed successfully.
You can see at 16:00:56 Server Manager got a call from Time Machine to start the services backup and finished at 16:09:26. Open Directory would have been backed up during that process. Take a look at /private/var/log/hwmond.log
serveradmin$ tail /private/var/log/hwmond.log
Tue Jun 4 16:08:36 BST 2013 - Number of drives change from 4 to 5.
Tue Jun 4 16:08:48 BST 2013 - Number of drives change from 5 to 4.
You'll see that both drive change warnings from Server Monitor occured just before the services backup completed. You can also use the sudo diskarbitrationd -d command along with tail /private/var/log/diskarbitrationd.log in another terminal window, trigger a Time Machine backup manually and watch this disk image mount during the backup process. Compare the mount times with the above logs to see if they all match up.
Although I have discovered the cause (which thankfully seems harmless) I have not discovered a way to stop it from generating pointless alerts. I'll post here if I figure it out. I am in the process of upgrading all of my servers to Mountain Lion so it may be a moot point. I am hopeful this information may help someone out there even though it is thoroughly out of date.
Scot
