I’ve been going back and forth from one storage solution to another ever since deciding to purchase Panasonic’s Lumix GH4. Not only will the 4K files require far more storage capacity than HD, they will also demand faster transfer speeds. The iMac I ordered last month will be equipped with Apple’s Fusion drive, which, according to reviewers, has write speeds of around 320MB/s and read speeds (the numbers that matter for video editing) approaching 680MB/s, which should be plenty fast for offline editing in 4K. As for what external drive to pair up with the iMac, my heart started to race when I read about LaCie’s stylish new Little Big Disk Thunderbolt 2, a portable drive housing two Samsung SSDs and capable of speeds exceeding 1,100MB/s when connected to a Thunderbolt 2 port. Since the 2013 iMac only sports the original Thunderbolt, speeds would be somewhere in the 800MB/s range: not too shabby! But the 1TB drive will retail for a whopping $1,299. So when I learned about the WD My Passport Pro with Thunderbolt interface, my ears perked up. First of all, the unit is the fastest portable disk drive to date, reaching speeds upwards of 200MB/s – sufficient for doing offline editing of 4K, but a far cry from saturating the protocol. Moreover, the drive comes in two flavors: 2TB and 4TB, the former costing $300, the latter, $430 – a roughly $900 savings over the LaCie. And best of all, the WD drive is bus powered, making it truly compatible with rMBP laptops. The WD My Passport Pro chassis is constructed of aluminum and is supplied with an attached Thunderbolt cable.