156 of 164 people found the following review helpful
Can be used as an external boot disk on a Mac,
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This review is from: WD My Passport 2TB Portable Hard Drive - Black (Personal Computers)
Even though there is every reason to expect any external hard drive to be usable as a boot disk on a Mac, these days some manufacturers perform tweaks to their drives (such as omitting certain components from USB controllers to further reduce the size of the drives) that inadvertently prevent them from being bootable on a Mac.
Samsung's S2 portable drives and even some of Western Digital's own FireWire drives come to mind.
Prior to buying this drive, which at the time of this review is currently the only widely available 2TB USB 3.0 bus-powered portable hard drive, I was unable to find any information online about whether it boots a Mac, so I finally decided to try it out for myself.
I am happy to report that this drive (Western Digital My Passport 2TB USB 3.0 Portable Hard Drive) can indeed be successfully used to boot a Mac, via both USB 2.0 and USB 3.0.
For best results (and especially if booting is required) on a Mac, you'll need to first format the drive using Apple's Disk Utility, as with other drives that have not been pre-formatted for the Mac. This can take from under a minute to a couple of minutes at most.
If desired, Disk Utility can be used to create multiple partitions on this drive, one or more of which can be made bootable by either installing OS X onto it, or cloning an existing bootable partition.
Hope this helps others who may be looking for this information before their purchase.