How can I regain access to files on external Mac hard drive?

Anonymous November 17, 2013
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I have a MacBook Pro with Lion installed version 10.7.5. I also have a WD 3TB external hard drive with Firewire and USB. When i open the external drive in Finder I can see some folders but all of these folders have invisible contents, as in, when I click to open the folders the drive opens it but then starts to whirr and make sound and nothing shows up even though there would normally be around 6000 photos organised by date into separate date folders. I tried Verifying and Repairing in Disk Utility but both came up with an error about the B-Tree node being invalid in size or something. It then immediately told me to backup and format the drive. I obviously don’t want to lose the images so I didn’t format it, and i can’t back it up if I cant copy over the files to another drive (because I can’t even see them). There may be a problem with permissions, for example when I click Get Info it sometimes, and I emphasize ‘sometimes’, shows that I can only read, not write. Other times it says read and write so I’m confused. You should know that when I select the drive in Disk Utility it does seem like my data is there. It says 280GB have been used. I’m sure not all of that is indexing space. Methods I’ve been wanting to try would be to restore the permissions on the drive. I’m not very experienced with Terminal but I’d be happy to paste some code in to restore permissions if you think it’d work. I have also been considering buying DiskWarrior because maybe I need my directory rebuilt inside the drive (Hopefully I’m getting this terminology correct). Any help you can give me would be greatly appreciated. Thanks :)

  1. Kemmy K
    November 20, 2013 at 11:07 am

    Guess you've tried a lot to get access to your external hard drive.
    I've met a similar trouble as you and I did not try your method.
    Instead, I used a mac recovery software to get my data in my external hard drive by saving data on my computer and format it. Then I can reuse it again. You can find it here:
    Hope it can help you. :)

  2. Hovsep A
    November 17, 2013 at 7:59 am

    perhaps Testdisk can help?

    Open Terminal in the Utilities folder.
    sudo chflags 0 /volumes/*
    sudo chmod a+rx /volumes/*
    killall finder

    • Bruce E
      November 17, 2013 at 8:26 am

      The errors thrown are not indicating permissions issues, but errors in the metadata B-tree nodes. Attempting to change anything, including permissions, in this state may cause additional corruption. The metadata MUST be fixed before attempting anything else resulting in changes on the drive. It is also why I suggested remounting the affected drive in read-only mode before even attempting to create an image to work with.

    • Hovsep A
      November 17, 2013 at 11:19 am

      reasons for B-tree nodes error can be multiple:
      •File system corruption, library files, or hard disk profiles.
      •Node structure corruption.

      does /sbin/fsck –fy can help?

      Fixing invalid node structure in a Mac OSX (w/o having to buy software!)

  3. Bruce E
    November 17, 2013 at 7:08 am

    Your first step should be to unmount the drive and mount it again in read-only mode. Next, image the entire drive. You can use the dd utility for this - check your man pages to see the exact format of the command since I don't know if or how Apple has modified it for OS X. You will need another drive of the same (or larger) size in order to do this. All of the following operations should only be done on the new drive image, not the original.

    The B-Tree error you are seeing has to do with how the directory and file metadata is stored on the drive. You will need a utility that understands the HFS+ file format to try to repair this. You may be better off attempting to run some HFS+ recovery tool to try to save everything that can be accessed without errors first. After that has been done, you can start trying the higher-risk operations in order to try to fix your invalid node errors.

    Because these errors are with your metadata, it is likely there will be some amount of data loss even if it is brought to an expert for recovery (which is also very expensive).

    Sorry, I can't provide information on specific tools to use since I don't use Macs myself and have not had to try to do any kind of HFS+ recovery operations, although there are books such as Backup & Recovery (published by O'Reilly, ISBN 0-596-10246-1) that covers some recovery operations that may work for you in this instance. I have not read those chapters, but merely skimmed over some of the high points, but their chapters on Unix, Linux, and Windows systems cover some of the same capabilities.

  4. Rich P
    November 17, 2013 at 7:03 am

    I bought DiskWarrior and after about an hour it had created a new directory and saved the day. The drive is damaged somehow but i got my files back and am backing them up to 3 different external hard drives as we speak. Not buying WD ever again. I've had multiple problems with them over the past 2 years. Too much stress. Hopefully my new Seagate drive will work a treat.

    • Bruce E
      November 17, 2013 at 7:28 am

      Doesn't matter who manufactured 'em, you will always have hard drives with issues. I use a mix of WD and Seagate since I have had the least amount of trouble with them and when I do, getting them RMA'ed is simple and fast. I have never had an RMA denied by either company and they both cross-ship for me. In one case, WD was no longer making the same model drive as the one that failed so they replaced it with a larger drive. Also, the replacements have almost always been new, not refurbished or remanufactured.

      The last time I had a WD drive fail was around 3 years ago. My latest Seagate drive developed a huge issue with bad sectors about 3 months ago. I ended up using Hard Disk Sentinel Pro to get that one fixed up after spending 4 days moving files to a new drive. I only lost 4 files (just over 1 GB of data) from a very full 1 TB drive. The drive is now functioning error free (though with a lower reliability rating) as an emergency drive for very temporary storage.

    • Oron J
      November 17, 2013 at 10:50 am

      Glad to hear your problem is solved. DiskWarrior is awesome. I've used it on many ocassions and it saved the day. However, it's important to understand that it only deals with rebuilding data structures on the hard disc. It does not address hardware problems and is unlikely to recover data when hardware is the cause of the problem. This sugests that your problem was not caused by WD. Indeed, the failure rate for all hard drive makers (there are only about 5 of them) are very similar, and although hard drives do fail from time to time, file-system problems are probably a more common source of faults then hardware ones.

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