The Western Digital (WD) VelociRaptor name originally came from WD’s line of high-performance hard drives which are pro-summer/enthusiast version of drives typically used in servers etc. Instead of rotating at 7200rpm, those drives could spin at 10,000rpm, which made data seek times much better.
The Western Digital VelociRaptor Duo is an external Thunderbolt case that contains two such drives, and the combined maximum capacity is 2TB (2x1TB). Each VelociRaptor Duo box has additional Thunderbolt connectors so that users can “daisy-chain” drives to add additional capacity or simply connect more Thunderbolt devices.
The two 10k drives combo won’t beat SSD drives in terms of random access times or peak transfer rates. However, traditional spinning disks still do a great job with sequential access. Jobs involving big files like video editing may run efficiently with this. Also, even at a $899 price, it remains competitive against SSDs which would run for more than $4000 for a 2TB capacity.
And pricing is what the whole point is: with a 2TB capacity, SSDs become extremely expensive or very complex to handle (you could always try to “RAID-0″ many 512GB SSDs). so if you have a workload that doesn’t rely on random access too much, the WD VelociRaptor Duo could be a very decent solution.
Alternatively, you could also get the same performance by buying your own Thunderbolt enclosure and two Western Digital VelociRaptor WD1000DHTZ drives. They go for $260 a piece on the web, so that leaves you with $380 left to find a proper Thunderbolt dual-enclosure… I have not tried it, so make sure that the 3.5″ fit, but in theory, it should work.