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TOPIC: External drive rebuild error

External drive rebuild error 29 Jun 2017 10:30 #8425

Please advise me on Error in screen shot.

This is my old drive from this machine it got stuck doing a surface scan and I couldn't resurrect it directly so I replaced the drive and reinstalled the OS, but I still need to migrate by data from the old machine. It was previously doing a volume optimization when it quit mid moving a large quantity of data, if memory serves right 10GB. A subsequent surface scan started throwing up over 2500 bad blocks before I quit and ran for five days before I quit to.

The data is in the directory but copying yields sudden cessation of copy, when a fragment cannot be found.

Please tell me the procedure to attempt rebuilding the disk and why Techtool says it is running from that disk too.
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External drive rebuild error 29 Jun 2017 12:42 #8426

Thanks for your clear and detailed report.

I have seen one or two other reports of the program apparently misidentifying the volume from which it is being run. If you want to investigate that, please send a message to This email address is being protected from spambots. You need JavaScript enabled to view it. , including a link to this thread. You will receive a reply by email.

It is likely that the optimization failed because of the large number of bad blocks on the drive. It is unlikely that you are going to be able to rebuild the disk directory with TechTool Pro, because it creates a new directory, and must write that directory to the volume in such a way that the disk directory files (Catalog B-Tree and Extents B-Tree) must each be written in a single piece. That process may encounter bad blocks. I suggest that you try manually copying as many files as you can from the volume, using a cloning tool such as Carbon Copy Cloner. I suggest you read about how it handles errors during copying. After you have copied as much data as you can from the volume, you could try repairing the disk directory with Disk Utility, which writes only to the disk directory entries that need changes. That smaller number of writes is more likely to succeed than the larger number of writes needed to replace the entire disk directory.

The drive with the bad blocks should be replaced. The details about bad blocks are in this posting:

Surface Scan
MicroMat Inc
Makers of TechTool
Last Edit: 29 Jun 2017 12:45 by micromattech3.
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External drive rebuild error 29 Jun 2017 18:42 #8427

I am running CCC and it is taking forever to copy from the Applications menu. But I am going to leave it running now and go to sleep.
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External drive rebuild error 29 Jun 2017 19:25 #8428

It is not unusual for it to take a long time to copy data from a volume with so many bad blocks.

One of the reasons I suggested that you look into Carbon Copy Cloner was my recollection that it can use multiple copy engines, and if one fails, it will attempt to copy the data with another copy engine. Of course, if the problem is that the data is simply no longer there, because the magnetic media has flaked off the platter, all of the copy engines will fail, and the entire process will take a long time.

Getting enough sleep is a really good idea. Dealing with a situation such as your failing drive is stressful, and lack of sleep can contribute to errors one would not normally make.
MicroMat Inc
Makers of TechTool
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External drive rebuild error 01 Jul 2017 00:18 #8429

The Carbon Copy crashed too. And now I can't even find a few files that were previously copied before the second attempt.

So now I tried to rebuild the partition and they tell me its going to nuke the drive. Doesn't serve my purpose. Disk Utility got so far along and then quit. Incomplete at the tail end. So now it seems I need to copy the data as is off the drive in chunks and then mine it for files at a later date.

So could you please advise me what software to get for that? Something that will just copy data as read from the drive and dump it on to another? Ignoring content. Just blindly?
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External drive rebuild error 01 Jul 2017 00:44 #8430

Thanks for getting back to us. I have wondered how you were doing.

DO NOT attempt to repair the disk directory of this volume, or make any changes to it.

The unfortunate fact is that copy engines are not designed to handle large numbers of unreadable blocks. The Volume Cloning tool in TechTool Pro makes use of a Unix-based copy engine that copies blocks, one after another, from a source volume to a destination volume. Because it copies blocks, rather than files, it requires that the destination volume be at least as large as the source volume. That way, even the free space from the source volume can be copied. I asked a colleague what he thought would happen if the Volume Cloning tool encountered a large number of bad blocks, and he thought it would stop.

I suggest that you contact the makers of both Carbon Copy Cloner and Super Duper! and ask about a Unix command line tool that will ignore errors and proceed to the next readable block. I have not encountered a case quite like yours before, which is why I do not know the answer in advance. What you need is a tool that will copy files, but will not be halted by many unreadable bad blocks. Copying files requires a disk directory that is free of serious errors.

The Unix tool dd will copy blocks from one volume to another, but that just gets you a copy of your damaged volume:

hints.macworld.com/article.php?story=20050302225659382
MicroMat Inc
Makers of TechTool
Last Edit: 01 Jul 2017 00:56 by micromattech3.
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The following user(s) said Thank You: aguntala

External drive rebuild error 01 Jul 2017 01:00 #8431

You are welcome.

There is no way to know the distribution pattern of the unremapped bad blocks in relation to the files. There is also know way to know whether the physical process that caused the unremapped bad blocks is continuing, or whether the magnetic media is stable, for now.

I suggest that you try copying your user folder to another volume on another device. Reinstalling the system software and applications manually is tedious and time-consuming, but we need to make sure that you have made every effort to back up the files you created yourself, the ones you cannot replace by running an installer, by however tedious a method. Try to back up your most important files, such as financial database files, your Apple Contacts, your email, photographs etc. If backing up a large folder with subfolders fails, try the subfolders, one at a time.
MicroMat Inc
Makers of TechTool
Last Edit: 01 Jul 2017 01:06 by micromattech3.
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External drive rebuild error 01 Jul 2017 01:19 #8432

Some of the files you need to attempt to back up are in the Library folder for the system and the Library folder for the current user (indicated by the ~ character):

Using the Finder's Go To Folder feature, in the Finder's Go menu, paste in these paths, one at a time:

/library/application support

~/library/application support
MicroMat Inc
Makers of TechTool
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