Download the WD Discovery software for Mac from the Western Digital site. Use a Mac with an older release of Mac OS to format your WD Passport drive. This is particularly necessary for purchases of generic PC drives, which almost always come preformatted to be Windows compatible rather than for Mac OS X. If you want to insure full Mac compatibility of a new external hard drive or flash disk, you’ll want to format the drive to the Mac OS Extended filesystem. I eventually managed to erase/format the new drive using disk utility on an old iBook G4 running OS X 10.4.11. Just bought a new Elements 4Tb and when I try to erase/format the drive using Disk Utility the erase fails with “mediakit reports not enough space on device for requested operation” I have an older WD 4Tb drive which works fine on my iMac. Yes, it had some software specifically made for OS X on it, but even that didn. When I bought the WD My Passport Ultra drive, I was surprised to see that it didn’t support OS X out of the box.

Out of the both it's not Mac compatible, but you can format it for use with your Mac in just a few minutes. Tutorial on how to format a Western Digital Elements Harddrive for a Mac.

How to format wd elements for mac os x