If you have lots of data to transfer, the WD 2.5" My Passport Ultra for Mac 4TB Silver external HDD is just what you need, giving you up to 4000 GB of portable space. This is enough to back up large amounts of HD and 4K content. 2.5" drives are designed chiefly for people who want to have their data always at hand. One great advantage of HDDs is their large capacity and comparatively low price. On the flipside, these drives use mechanical parts that are prone to damage if exposed to some rough handling. The Western Digital external storage uses USB 3,2 Gen 1 (USB 3,0) and USB-C interface.