I imagine most people have a portable hard drive, rather than an external one that has its own power supply, for their laptop. My iMac has a 1 TB drive specifically for Time Machine, but I was thinking of getting a 320-500 GB portable drive for my MBP. Can I partition part of it for TM and use the rest for storage? I was looking at the WD Passport drives and also a portable Hitachi one. Anyone have these external drives, and are they compatible with Macs ? Do portables fail more often than external drives that don't get moved around a lot?