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

Taken from Adam Nash’s blog Psycohistory. I apologize for not giving credit more explicitly when I first posted the article.

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.

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


  1. I wish I had seen this post before I started trying to reformat the drive. I am trying to reformat the 1TB MyBook and seem to be in an endless loop – that says newfs_hfs: /dev/rdisk1 size is not a multiple of 4k.

    I cannot exit from the disk utility screen, and I don’t think anything is happening. I don’t want to force quit – unless I have to – might damage the drive.

    Anyone have any suggestions? ASAP? thanks

  2. Adam,
    I’m sorry for not being more explicit with credit line. I use this site as more of a notebook than anything else… I really don’t expect (and my visitor numbers prove it) anyone to actually visit. Just say the word and I’ll drop the article from the site.

  3. Why is there a problem of formating . Is this after one runs the setup file of western digital tb1. If one reformats as soon as purchesing hardrive by right click and hit quick format it does it in 5 seconds. I did not run setup file . What is in it?

  4. I hit left click quick format and was don’t in 5 sec. Do You have problems when one has already run set up of hardrive What is in setup file? I copied and past all information sent with tb1 to different hardrive in another folder . Didnt know if I wanted it latter.

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