Time Machine. Backup failed with error code: 21

It appears Im having a similar problem, and hopefully one more user's woes may lend support to Apple resolving this issue. Im running 10.5.4 now and a week or so ago TM on my Time Capsule started failing. Here’s the latest log:

9/18/08 10:47:39 AM /System/Library/CoreServices/backupd[1873] Network volume mounted at: /Volumes/Time Capsule Disk-1
9/18/08 10:47:41 AM diskarbitrationd[44] unable to repair /dev/disk3s2 (status code 0×00000008).
9/18/08 10:47:41 AM kernel hfs swapBTNode: invalid node kind (56)
9/18/08 10:47:41 AM kernel node=0 fileID=8 volume= device=/dev/disk3s2
9/18/08 10:47:41 AM kernel HFS: Runtime corruption detected on , fsck will be forced on next mount.
9/18/08 10:47:42 AM /System/Library/CoreServices/backupd[1873] Failed to mount disk image /Volumes/Time Capsule Disk-1/JBBComputer_0016cb8ab7dd.sparsebundle (DIHLDiskImageAttach returned: 109)
9/18/08 10:47:42 AM /System/Library/CoreServices/backupd[1873] Giving up after 3 retries.
9/18/08 10:47:47 AM /System/Library/CoreServices/backupd[1873] Backup failed with error: 21
9/18/08 10:47:47 AM kernel AFP_VFS afpfs_unmount: /Volumes/Time Capsule Disk-1, flags 0, pid 1944
9/18/08 10:47:47 AM /System/Library/CoreServices/Finder.app/Contents/MacOS/Finder[147] StatusMonitor::volumesChangedCallBack returned -47
9/18/08 10:47:47 AM /System/Library/CoreServices/backupd[1873] Ejected Time Machine network volume.

Any ideas? Cheers!

I'm seeing the same problem, have been for a few days now. I've tried a few things, like turning TM off and on, reselecting the backup drive etc. 😟

James,

It would appear this error lies in the way TM is trying to mount the volume, specifically that Volume_1, the DNS-323 volume name, is not owned by TM. TM then tries to create a new volume, Volume 11 and stick the sparebundle on it.

Is there a way of making TM "own" the volume, Volume_1?

Actually, it is not TMs failure to mount the volume that is causing your failure to backup. I have received the same Console message using a Time Capsule. However, Time Machines' attempt to 'remount' the volume always succeeds and the backup goes through. That appears not to be your experience, but it is NOT because the volume is not being mounted. It is.

*Mount Point Conflict (TMDisk-1)*
NOTE: the following distinguishes “network drive” (the physical hard disk) from “disk image” (the sparsebundle file TM uses to backup to).

First of all, I am convinced that the second mount point that is created (in your case Volume 11) is due to the fact that you already had the network drive mounted on your desktop at the time of the attempted backup. Was that the case?

When you manually mount a network drive the system creates a mount point in the /Volumes folder (Let’s call it TMDisk ). While that exists any attempt by Time Machine to mount the same disk will created a second mount point ( TMDisk-1 )

Nevertheless, as I have observed, this doesn't seem to prevent backups from taking place successfully, at least on the Time Capsule. And according to your Console logs it appears that your volume is being ‘remounted’ successfully.

*”The Backup Disk Image Could Not Be Mounted”*
The real issue is Time Machines' failure to mount the disk image (sparsebundle) contained on your network drive.

+Failed to mount disk image /Volume/Volume 1_1/MacBook001b6334c307.sparebundle+
+Backup failed with error: 21+

More often than not this is due to having the Time Machine backup disk image (sparsebundle) mounted on your desktop during a backup attempt.

Eject the backup disk image (sparsebundle) by either clicking the little Eject icon to the right of the disk image in the Finders’ Sidebar, or Ctrl-Click the drive icon on the desktop and select “Eject” from the contextual menu. Now try backing up again or launching Time Machine to view previous backups.

For more information, see an article on this here:

[http://discussions.apple.com/thread.jspa?threadID=1715977]

Alternatively, a backup disk image can fail to mount if there is a problem with your computer name.

*Proper Computer Name* #
Make sure your computer has a proper name. Go to System Preferences --> Sharing. Time Machine needs to differentiate your computer from others on your network (i.e. "Bills MacBook" or "Office iMac"). If the "Computer Name" field is blank, create a name. Realize that if this step is necessary, you will likely have to start the Time Machine backup process over again and do another full initial backup.

According to THIS article [http://support.apple.com/kb/TS1760], Time Machine may experience problems if your computer name includes certain characters. Make sure the computer name only includes ASCII characters from the following set.

(0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ)

Once a change in the computer name occurs, you should stop and restart Sharing on the affected computer. Uncheck and then recheck Sharing in the Services list on the left.

Let me know if any of this helps.

Cheers!

Try this:

Stop backing up by choosing none and and then stop backing up in time machine preferences.
then
Open up Keychain Access, then open up the System Keychain and them remove anything that says *.localhost, there should only be one thing with your Time Capsule name in it. after removing that start your time machine by choosing the Time Capsule disk and backup.

Hope this works for you as well as it did for me.
Alex

I had suffered from the problem of my backup failing. I finally discovered that if I unplug my external HD and re-try it, all goes as planned. Not sure what is going on but it has worked for me.