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TOPIC: Rebuild Error Encountered Precheck Failed

Rebuild Error Encountered Precheck Failed 09 Jul 2016 11:59 #7339

I'm trying to get access to a TimeMachine disk. The disk doesn't mount. It's been in use for only a couple of months. When I run TechTool pro v8.0.5 I receive the following error: Rebuild Error Encountered
Precheck Failed.
Here is all that's in the reports

Volume Structures

Completed:Volume:Jul 8, 2016, 8:37 PM"My Passport for Mac"
FAILED
Validation Error Encountered
Catalog File
The Volume Structures test checks the integrity of a volume. These data structures keep track of where every file and folder resides on a volume.

Volume Rebuild
Completed:Volume:Jul 8, 2016, 9:54 PM"My Passport for Mac"
FAILED
Rebuild Error Encountered
Precheck Failed
The Volume Rebuild tool reconstructs a volume's disk directory in order to make it more efficient or to repair volume corruption.

Any suggestions about a next step?


Stephen
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Rebuild Error Encountered Precheck Failed 09 Jul 2016 14:02 #7340

It is unlikely that the Volume Rebuild tool will be able to rebuild the disk directory of a typical Time Machine volume.

The disk directory of a Time Machine volume containing N backups can be N times larger than the directory of the source volume, assuming that not many files have been deleted as the source volume is used. The Volume Rebuild tool must be able to hold the new disk directory files, the Catalog B-Tree and the Extents B-Tree, in RAM, simultaneously. Few users with large volumes have enough RAM for that to be possible.

The only suggestion I can make is to run the Surface Scan to check the drive containing the Time Machine volume for unremapped bad blocks. If it passes, you can make a new Time Machine volume, but of course, it will not have older versions of files in it.

For future reference, I think it is a bad strategy to rely on Time Machine as an only backup, if that is what you are doing. Time Machine is wonderful when it works properly. Without it, I would have lost my Yojimbo database, which was corrupted upon saving and quitting. The good backup in a clone was immediately replaced by the new, corrupted file, because I wanted to have a backup of my new work, which I promptly made using Super Duper. Despite the limitations of clones, I think it is prudent to have one in addition to Time Machine.

Please see the impolitely-titled but well-thought-out article:

11 Stupid Backup Strategies
MicroMat Inc
Makers of TechTool
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Rebuild Error Encountered Precheck Failed 09 Jul 2016 17:43 #7341

There are only 2-4 time machine back-ups as this was a new computer. Due to a keyboard problem Apple replaced it and I was going to restore it from Time Machine.

The surface scan doesn't find any problems

Are you telling me I've lost absolutely everything?
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Rebuild Error Encountered Precheck Failed 09 Jul 2016 18:10 #7342

I do not know of any way to repair the disk directory when the Volume Rebuild tool does not work. You can inquire further about this issue by sending a message to This email address is being protected from spambots. You need JavaScript enabled to view it. . You will receive a reply by email on Monday.

If the computer is new and you have AppleCare, it is possible that Apple could look into the problem with the Time Machine volume not mounting. If it is your only backup, I suggest you leave it alone until someone looks at it.

Sometimes a restart is all that is needed for a volume to be able to be mounted, because the operating system makes a repair to the partition map during the restart.
MicroMat Inc
Makers of TechTool
Last Edit: 09 Jul 2016 18:13 by micromattech3.
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