Time Machine reverts to Macintosh HD after external drive is ejected

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Time Machine reverts to Macintosh HD after external drive is ejected

I've seeing a problem with Time Machine with one of my external drives. Here's my setup:

MBP 15"
OSX 10.7.4
Work external drive - Seagate GoFlex, via USB
Home external drive - Western Digital Green, via USB

I had been using both home and work drives as Time Machine backups, and things were working fine. I would have to re-designate the appropriate Time Machine backup drive when I changed locations, but everything was working.

The problem:

When I attach the work drive and point Time Machine to the drive, it works. When I eject the work drive, the Time Machine prefs panel shows "Time Machine - work" in greyed out text as the target drive, reflecting that the drive is not available.
When I attach the home drive and point Time Machine to the drive, it works. But when I eject the home drive, the Time Machine prefs panel shows "Macintosh HD" in normal text as the target drive. Worse, I think it actually attempts to back up to the internal drive, because at the next Time Machine backup interval, I get a "The identity of the backup disk has changed" error from Time Machine.

I've tried a full reset of Time Machine by deleting the prefs file. I've also tried verifying the home external disk. The problem persists. Any help would be greatly appreciated.

MacBook Pro (15-inch Mid 2010), Mac OS X (10.7.4)

Posted on May 17, 2012 11:05 AM

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Answer 1

softwater

Level 5

5,556 points

May 17, 2012 11:12 AM in response to stevekim

I'd be more inclined to think the problem is with the Western disk than with Time Machine.

Have seen a lot of problems reported with Western Digital disks and Lion. Do you have another spare disk you can replace and test it with for the home drive?

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Answer 2

stevekim Author

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May 17, 2012 11:21 AM in response to softwater

Totally possible. I can't imagine why Time Machine would revert back to the internal HD upon external eject; maybe a bad/incomplete dismount of the WD drive is the culprit. I'll first try to reformat the WD drive and then try a different drive altogether.

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Answer 3

Linc Davis

Level 10

209,535 points

May 17, 2012 11:48 AM in response to stevekim

Do you have a folder named "Backups.backupdb" at the top level of "Macintosh HD"? If so, delete it.

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Answer 4

Pondini

Level 8

38,863 points

May 17, 2012 4:26 PM in response to stevekim

stevekim wrote:

. . .

But when I eject the home drive, the Time Machine prefs panel shows "Macintosh HD" in normal text as the target drive.

That's extremely unusual, but has happened to a couple of other folks (I've seen two that posted here). How and why it happens is a complete mystery.

First, as Link recommends, if there's a Backups.backupdb folder at the top level of your internal HD, delete it.

A full restore from Time Machine fixed it for one of the other users (why is another complete mystery). If those are your only backups, I'd advise making another, on a different HD, probably via CarbonCopyCloner or SuperDuper, "just in case" something goes wrong with the restore.

I'd recommended reinstalling OSX, on the theory that something there was damaged, but the user had already done the full restore and fixed it.

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Answer 5

stevekim Author

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May 18, 2012 6:15 PM in response to Pondini

I did indeed have the /Backups.backupdb folder, but deleting it did not solve the problem. I thought that was the local backup folder (disabled by executing "tmutil disablelocal")?

Reformatting the WD Time Machine partitiion and resetting Time Machine (turning off TM, deleting the prefs file, restarting) seems to have fixed the problem, though.

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Answer 6

Pondini

Level 8

38,863 points

May 18, 2012 6:47 PM in response to stevekim

stevekim wrote:

I did indeed have the /Backups.backupdb folder, but deleting it did not solve the problem. I thought that was the local backup folder (disabled by executing "tmutil disablelocal")?

No, Local Snapshots are in a hidden .MobileBackups folder. The /Backups.backupdb folder was created by Time Machine trying to make actual backups to the internal HD.

EDIT: See Time Machine - Frequently Asked Question #30 for the gory details.

Reformatting the WD Time Machine partitiion and resetting Time Machine (turning off TM, deleting the prefs file, restarting) seems to have fixed the problem, though.

Curious. Keep an eye on it, especially when the backup drive isn't available, and a backup is scheduled. That seems to be when the trouble starts.

From your first post:

I had been using both home and work drives as Time Machine backups, and things were working fine. I would have to re-designate the appropriate Time Machine backup drive when I changed locations

Stay tuned on that one. The rumor sites say that can be automated in Mountain Lion. See the last point in the How it Works section here: http://en.wikipedia.org/wiki/Time_Machine_(Mac_OS)

Message was edited by: Pondini

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Answer 7

stevekim Author

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May 18, 2012 10:56 PM in response to Pondini

Thanks for the clarification on Backups.backupdb, and thanks for the heads up on Mountain Lion's handling multiple TM targets. I was thinking of messing around with multiple prefs files and MarcoPolo for automatically switching then in/out, but I'd prefer to just wait for the feature to *hopefully* show up this summer.

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