The Secret to Reformatting a Western Digital WD 1TB My Book External Hard Drive

Little tidbit.

When you buy a Western Digital (WD) 1 TB My Book External Hard Drive, they usually come formatted for Windows using FAT32. Of course, if you are using it with a Mac, then you’ll want to reformat it using Mac OS Extended (HFS+).

The problem: When you try to reformat in Disk Utility, you’ll get a very cryptic error that says that there was an unknown error with the partition map.

The solution: If you go to the partition map and click the “Options…” button, you’ll be able to select which scheme to use for the boot records. It turns out, if the boot record scheme is set to “Master Boot Record”, you will not be able to format it as Mac OS Extended. Flipping it to GUID or Apple Partition Map will work.

Once you get to that magic dialog, it’s pretty clear what to do. Why Apple doesn’t communicate this error intelligibly when you attempt to format I don’t know.

In any case, there is an Apple Discussion Board thread that saved the day for me. I’m posting it here just in case it saves the day for someone else.

I’m now ready to try out Apple Time Machine for the first time…

Update (12/29/2008): It’s amazing, but this continues to be one of the most popular posts on this blog.  Everyone seems to have this problem.  Interestingly, it’s not unique to Western Digital drives.  I find that I need to do this with Maxtor and Seagate Free Agent drives also.  I just did this with the new Seagate FreeAgent 1.5 TB external.  Works like a charm…

50 thoughts on “The Secret to Reformatting a Western Digital WD 1TB My Book External Hard Drive

  1. Thanks, I just bought a Western Digital My Book Essential 500GB about 10 minutes ago on and am currently using a Black MacBook running Tiger 10.4.11. Im hoping this post will prove very useful when the hard drive arrives and I get started using it as I have been warned by some other users about formatting problems regarding this external hard drive. I will bookmark this page and hopefully everything will be ok when it arrives. Thanks in advance.

  2. Thanks alot, I had this same problem with a Buffalo TeraDrive and they had know idea what the problem was. Todd

  3. Thanks that is such a lifesaver. Spent ages working out what the problem was! Why apple decided to use such a cryptic error message I don’t know, and there is no mention of this issue on the WD website, for some reason unbeknown to me.

  4. Adam,

    So MANY thanks, I can’t tell you how much hair I was about to pull out trying to format my 1Tb drive! Just bought it today, and was beginning to think I would have to take it back to the store.

    I too am looking forward to using Time Machine – hope it works OK now!

    Happy New Year to you – you’ve made my day!


  5. Wow! Am I glad I uncovered your tip. I just spent a whole day trying “zero out” and reformat an external 640 GB WD drive & I have a 1 TB WD drive awaiting putting in my Mac Pro (gotta take out a smaller one :).

    Your simple tip reminds me of the old idea that you have to pay an expert a fortune to do two minutes work, because he spent many, many hours learning how to do that thing in two minutes.


  6. Thanks for putting this tip out there. I figured it out myself last night, but the solution was more serendipitous than skill.

    I am guessing that WD doesn’t put this out there because they want to promote the extra crap demo software that comes with the drive.

  7. thank you so much! just spend a while trying to figure this out, and your solution worked perfectly! thanks again!!!

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  9. Many thanks – 5 mins searching the web after 2 hours of zero progress with Disk Utility and my new terabyte drive is reformatted, and ready to use.

  10. Huzzah! Yes, it is a popular post – for a reason. It works! Thanks for posting this. And, just fyi – this was the first search engine result on Google when I was looking for a solution. And well worth it.

  11. Thanks for the tip! Installing Snow Leopard tonight and couldn’t figure out why my external back up drive wasn’t mounting on the desk top. Was just about to take out back and shoot it before I found this tip.

  12. Well, this simple yet incredibly effecting manor in reformatting such an investment has proven itself AWESOME. I thank you for writing this article, if it is okay with you; I’d actually like to write an article on this as well. Thank you.

  13. Well i am very very unexperienced with computers and am having a lot of difficulty. How do I create a partition or get the partition map or whatever. I really want to start using this hard drive but i am not very experienced so if someone could help me out step-by-step i would be very greatful. Thanks

  14. If you had to choose between a Seagate, Western Digital, or a Samsung hard drive, which would it be? Which do you consider the most reliable out of them? I had a WD that went to crap on me after about 6 months, so I’m a bit leery of them.

  15. Thankyou So much, My housemate spent ages trying to get his to work, and with a little research this has helped me immensely, Although without his error first, I would have spent a long time trying to figure out what the problem was.

  16. I’m following all the steps including GUID and I’m still getting a failure error: permission denied. The info on the drive shows read and write permission for everyone (but the lock is greyed out). I have a 1TB and a 2TB and can’t format either. I’m on 10.5.1 intel based mac. Could my disc utility be bad?

  17. Thank you for sharing this, I was going bonkers trying to figure out what I was doing ‘wrong’. Merry Christmas!

  18. Thank you so much for this information! I was having so many issues. I have several smaller external harddrives from WD and when I bought this because it was Mac friendly… All the others were plug-in and go… I really appreciate it 🙂 Happy New Year.

  19. The easiest way to reformat a Western Digital hard drive for the MAC is to:
    1) plug in WD external drive to computer via USB
    2) go to System Preferences > Time Machine
    3) select disk
    4) choose the WD external hard drive
    5) click on Back Up
    6 a prompt will come up asking you to ERASE so the hard drive can be formated for a MAC


    Your external is now formated and ready to use.

  20. This is a great external hard drive for expanding your digital storage capacity. I was in need for added storage and wanted to go for the 2TB WD Elements External Hard Drive. I wasn’t really happy with the prices I was seeing for the 2TB hard drive, and that is when I decided to check up on the 1.5TB drives. WOW! I was amazed at the price Amazon was offering these drives and I got two of them. Yes, two! (My work requires that kind of storage space)
    I got 3TB worth of storage for the price of a 2TB External hard drive!

    That said, let us talk about the performance of these drives –

    1) Build and form factor – Nice sleek looking enclosures. All black, the sides are fingerprint magnets with a glossy finish. The top and bottom panels have a matte finish. Looks matter to me, even if it just an external drive. The microUSB and AC sockets are closely spaced with a small white indicator light besides them. All in all very compact, sleek, and aesthetically pleasing device.
    2) Performance – I am getting constantly good speeds on these drives. Reads at 30MB/s and writes at about 24MB/s, which is good and fast enough for my needs.

    As always, users have to be careful with all hard drives, internal or external. I am handling my drives with the utmost care. I don’t want to lose any important data.

    Finally, this drive is a complete value for money purchase. I say go for it if you are out looking for a large capacity external hard drive.

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  22. okay i am still having an issue, my bf put in my new hard drive, in my black Macbook, then i did the put in the disc, held down the c key bla bla, now I am at the part where it won’t recognise anywhere to save it , i go into utility and then disc utility and on the left side, i see, the maox instal disc 1 and two other hard drives, i pick one of them and see where i click option, but then nothing else, so not sure, I am ready to pull out my hair if anyone can help, i will check back, i will sign in with my twitter so if anyone can tweet me or something, I am going bonkers, thanks, i bought my hard drive at london drugs, its 500gb, i believe

  23. Adam: You saved me a load of grief. I ran into the error message head-on and quickly did a search and found your post. It could’ve been ugly and you prevented a really bad night from transpiring.

    Sincere thanks, Jake

  24. I realize this is an old post but I’ve gotten myself into quite a fix. I purchased a 1T WD external hard drive for my iMac 10.7.2 but didn’t format it or partition it. Due to a series of apparent blunders, I can’t access anything I’ve copied to the WD nor can I unmount it (either on this mac or any of my other macs) Disk Utility will not allow me to partition or erase the drive because it is unable to unmount the disk. I’ve closed all applications, rebooted the computer, the finder, etc.. there seems to be no interference as far as applications go and I’m completely flummoxed. Can you possibly help me figure this out?
    Many thanks,

  25. Thank you! I read all over about this GUID table but didn’t think to look under that ‘option’ tab…you saved me lots of Google time!

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