Resurrecting a Time Machine
A few days ago, my MacBook Pro welcomed me with this message:
Time Machine Error
The backup volume is read only
To select a different volume, open System
Preferences and choose Time Machine.
I’d seen this before, and it’s no big deal. The simple fix is to just reboot the Mac, so I that’s what I did. After a 5 second reboot (gotta love these SSD Macs), my Time Machine disk wasn’t mounting, though.
OK, no big deal still, just run Disk Utility to repair it. Disk Utility chugged away on it for an hour or so and then said something like:
Disk Utility cannot repair this disk.
Uh-oh. Now what?
Next up: DiskWarrior. DiskWarrior is a time-tested hard drive repair utility, but I’d been reading that even it often can’t repair Time Machine volumes. Apparently, Time Machine does some pretty oddball stuff with the filesystem that makes it both fragile and difficult to repair, yet somehow more efficient. I didn’t want to drop $100 to find out whether or not DiskWarrior would work on my drive or not, though. It’s just a backup drive, after all. So, I borrowed a friends copy to evaluate it.
My apologies to Alsoft. I know this is outside the license terms, but DiskWarrior really needs a “try before you buy” or demo version. If the demo would have worked, I would have bought it in a heartbeat to be ready for the next time.
Ultimately, DiskWarrior could NOT fix the drive — at least not completely. It first reported that the drive had a hardware failure:
Directory cannot be rebuilt due to disk hardwarefailure (-36, 2541).
Not willing to give up just yet, I dug a little deeper and found this page where Dr. Paul Gardner-Stephen discovered that DiskWarrior will give this and similar “hardware failure” errors if the disk is simply “busy”! Sure enough, a “ps -ef | grep fsck_hfs” revealed the process that was keeping my Time Machine disk busy, so I killed it and tried DiskWarrior again.
This time, DiskWarrior got a little further along in the repair — no “hardware failure” — but it stopped short again with this error:
The Directory of the disk cannot be rebuilt.
There is not enough memory. Restart from the DiskWarrior disc and try rebuilding again. Error code 2154.
Another quick search on Bing (yes, Google, see what you’ve driven me to?) found this discussion on the Apple forums where it seems pretty clear that this is a common issue with DiskWarrior and TimeMachine disks, and there is no workaround.
Until now.
Again, not willing to give up so easily, I ran Disk Utility again and it appeared to now be getting past the point in the repair process it was getting stuck on before!
At this point, I was exhausted and it was way past my bedtime, so I let it run overnight. First thing the next morning, I checked my MacBook Pro:
IT WORKED!
My TimeMachine drive was officially back from the dead.
6 comments on “Resurrecting a Time Machine”
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matt > 140 
Hey Matt,
thanks for the info. I am such a noob with this stuff. Can you explain the part where you killed the process in Terminal. Not sure I can figure that out. No clue what a “ps -ef | grep fsck_hfs” is!
Thanks,
Brian
If you follow the link immediately before it, you’ll get more info, but this is a command that says, “get a list of all the running processes but only show me the ones that have fsck_hfs in the description.” fsck_hfs is a utility for fixing file systems, and it will be keeping your drive busy — maybe the system is trying to fix the drive itself.
When you see the output of “ps -ef | grep fsck_hfs”, there is a number at the front — the process ID. Type “kill 12345”, replacing 12345 with the actual number of the process ID. Sometimes you have to go as far as “kill -9 12345” — which means kill it no matter what.
Matt, this post is a lifesaver. i just resurrected my 2 Time machine drives; one died yesterday and the other died several months ago and I was ready to ditch it because I had already tried everything but nothing worked.
Thank you so much!
Great post Matt – just gone through a failed directory with my Stardom RAID 5. Marc from Alsoft (Disk Warrior) deleted my fsck_hfs and the RAID popped back up on my desktop. This will now enable me to copy the Stardom media onto a new array before Marc checks the directory problem with the Stardom. Thanks for shining some light on this subject.
This is very useful information. DiskWarrior was reporting a hardware failure for my external drive but I used Activity Monitor to quit the fsck_hfs process which then enabled DiskWarrior to access the external drive and successfully rebuild the directory – giving me back full use of the external drive and with data intact. Thanks very much for taking the trouble to share this.
I had just installed a Time Machine back-up on an old iMac with 1 gig of ram. Afterwards I tried using Disc Warrior and kept getting “The Directory of the disk cannot be rebuilt. There is not enough memory…” After several attempts I found that the solution was to unplug the back-up drive from the iMac. Disc Warrior then worked normally. I had to use another Mac to rebuild the directory on the backup drive.