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Western Digital My Book Thunderbolt Duo 4TB review

Our Rating :
Price when reviewed : £440
inc VAT

Fast when writing small files, but large file performance is disappointing - still the quickest Mac external storage we've seen


2TB + 2TB hard disk, Thunderbolt, 165x99x157mm

Thunderbolt has been talked of as the next high-speed breakthrough for external storage, but we’ve not seen many devices with these high-speed ports. That’s partly because Thunderbolt ports are only found on a handful of Apple laptops. Mac owners will appreciate the extra speed, as the company is still refusing to equip its computers with USB3 ports.

Western Digital My Book Thunderbolt Duo 4TB

The silver finish will complement your MacBook

True to form, Western Digital’s My Book Thunderbolt Duo is a Mac-oriented device. The Duo in the name refers to the pair of 2TB hard disks inside that can be configured in RAID 0 or 1, with the former striping the data across the disks for improved speed and the latter mirroring it for heightened security. RAID 0 keeps the capacity of both disks but you’ll lose all your data if one disk fails, while RAID 1 halves the capacity but will tolerate the failure of one disk with all the data intact.

Other features also help to make the Thunderbolt Duo easier to use. Click the glossy button on top of the drive and the grilled lid swings backwards, with a small plate of metal protecting the top of the two hard disks. They’re easy to remove by pulling a plastic tab, and simply slot back into place. There are two Thunderbolt ports on the rear – one to connect to your Mac, and one to daisy-chain to another drive.

The main attraction, though, is the speed on offer from Thunderbolt, with Western Digital claiming that it’s twice the speed of USB3, with a theoretical throughput of a massive 10GB/s. That may be true, but Western Digital has chosen to install two of its 2TB low-power Caviar Green drives in the enclosure, and they’re a bottleneck when it comes to performance. Our file tests, rewritten to work in Mac OS X and run in the faster RAID 0 mode, show just how average the Thunderbolt Duo is in some tests: it wrote large files at 102MB/s and read them at 128MB/s, which is slower than the USB3-equipped Buffalo DriveStation Velocity 2TB, which recorded scores of 105MB/s and 152MB/s in the same tests. If you’re a USB3-less Mac owner the comparison is academic, but as Apple hasn’t ruled out USB3 for the future it’s worth knowing if you should hold fire for the time being.

Western Digital My Book Thunderbolt Duo 4TB

Two Thunderbolt ports, so you can daisy-chain it with other hard disks or monitors

Small file performance was better. The My Book wrote and read our collection of photo-sized files at 86MB/s and 93MB/s – a huge improvement on the Buffalo, which ran the same tests at 31MB/s and 43MB/s.

The My Book’s speed didn’t improve with RAID 1 enabled rather than RAID 0. With this slower-but-safe mode used, it wrote and read large files at 79MB/s and 102MB/s, and wrote and read small files at 56MB/s and 83MB/s.

Western Digital provides some Mac software with its drive. Numerous options are included in its WD Drive Utilities package: one tool can perform a media scan to detect bad sectors, a RAID management utility allows choosing between RAID 0 striping, RAID 1 mirroring and no RAID at all, and the drive erase tool is self-explanatory.

It’s a well-built, attractive and easy-to-use drive, then, but the My Book Thunderbolt Duo just doesn’t live up to the speeds promised by the Thunderbolt interface, with large file performance no better than USB3-based drives – the blame for that can be laid at the door of the slower, eco-friendly hard disks. Of course, it’s still the quickest drive you can get for a Mac laptop and its small file performance is certainly impressive, so if you back up thousands of photos or music files you’ll appreciate the difference.

Basic Specifications

Rating ***


Hard disk Western Digital Caviar Green
Capacity 2TB + 2TB
Formatted capacity 3620
Price per gigabyte £0.10
Disk size 3.5in
Interface Thunderbolt
Power connector External
Spindle speed 7200rpm
Cache 128MB
Seek time 8.9ms
Weight 2.2kg
Size 165x99x157mm

Buying Information

Backup software included WD Drive Utilities
Price £440
Warranty three years RTB

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