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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 Comments Post a comment
  1. jonny #

    thanks, i love you!
    who woulda known that

    February 28, 2008
  2. jpwm #

    brilliant. simple.

    thank you.

    now to unleash the time machine!

    May 27, 2008
  3. Daphne #

    Thanks! I never would have thought of this, and it worked like a charm.


    August 6, 2008
  4. Sim #

    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.

    August 26, 2008
  5. Todd #

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

    October 23, 2008
  6. Mark #

    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.

    December 25, 2008
  7. Pete W #


    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!


    December 27, 2008
  8. 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.


    December 28, 2008
  9. David #

    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.

    December 29, 2008
  10. victor #

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

    January 3, 2009
  11. John #

    Thanks heaps. I would not have worked this out in a month of Sundays!

    January 20, 2009
  12. NealSega #

    THANKS! I was about to return the drive…

    January 21, 2009
  13. Eric #

    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.

    January 24, 2009
  14. Adam – Nailed it. Props to you, my intelligent friend. You’re a godsend to Mac geeks worldwide. Cheers!

    February 28, 2009
  15. 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.

    April 16, 2009
  16. maxnepstad #

    You’re a lifesaver, thank you!

    May 17, 2009
  17. kollektor #

    Thanks, Adam. It might be simple but I never would have got there without this tip.

    June 16, 2009
  18. Juan Carlos Alicea #

    It still works. Thanks.

    July 3, 2009
  19. 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.

    September 21, 2009
  20. Galen #


    October 17, 2009
  21. 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.

    November 29, 2009
  22. R2 #

    Thanks for making my night shorter!!! Doing a backup before I install Snow Leopard…Merry Christmas!

    December 3, 2009
  23. Matt #

    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

    April 8, 2010
  24. 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.

    April 16, 2010
  25. THANK YOU!

    For once Mac is complicated. Who knew?

    May 19, 2010
  26. Ralphie #

    thanks so much – this definitely helped me alot😀

    May 22, 2010
  27. Your the man! Thanks

    May 30, 2010
  28. Jasmyn #

    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.

    August 10, 2010
  29. Thank you thank you thank you!

    September 23, 2010
  30. david c #

    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?

    December 2, 2010
  31. Julia #

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

    December 24, 2010
  32. Jules #

    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.

    January 3, 2011
  33. RJL #

    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.

    May 26, 2011
  34. brilliant on both the initial post and RJL …now to UNMOUNT is the issue… alas

    July 17, 2011
  35. 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.

    August 9, 2011
  36. Richard England #

    Kudos yet again! Worked with a WD 3tb drive

    August 23, 2011
  37. Gregory Jones #

    Thank you. I’m not going to say I love you, but I would friend you on facebook. Thanks, guy!

    September 2, 2011
    • I am having trouble with my black Macbook, have installed the hd, and that is where I sit, I tried to do it all my self, to save some money, but did you install the same thing by any chance, thanks

      October 23, 2011
  38. 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

    October 23, 2011
  39. 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

    November 18, 2011
  40. Sonya M #

    Thank you, thank you, thank you.

    November 22, 2011
  41. 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,

    January 31, 2012
  42. Arnie #

    Old post, but still effective

    February 20, 2012
  43. Landy #

    Many Thanks… worked like a charm

    March 27, 2012
  44. Scott #

    You helped yet another person with this post!!!

    January 24, 2013
  45. Julia #

    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!

    February 4, 2013
  46. salt #

    You helped yet another person with this post!!! again

    July 16, 2013
  47. Andie #

    Thank you! A million thanks! It’s incredible how this problem still persists!

    October 4, 2013

Trackbacks & Pingbacks

  1.   The Secret to Reformatting a Western Digital WD 1TB My Book External Hard Drive « Psychohistory by CRACKMAC.COM
  2. how can see what data is in an internal Western Digital hard drive without putting it into a computer tower?

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