One USB3 external hard drive candidate that was especially disappointing was the Sans-Digital TowerRAID TR4UT-BP.   I used Sans-Digital quite successfully for USB2/RAID Thinkpad backups, however I simply could NOT get their USB3 based product to work, and the problem was clearly not with the Thinkpad W520.  There appear to be problems with a number of emerging USB3 products, however the Thermaltake product, mentioned in the earlier post, I have had good success with.   To make matters worse with the Sans-Digital product; I was promised a refund, however I finally had to have the bank issue me a credit for the Sans-Digital charge.   Due to this experience, this is probably the last time I will purchase a Sans-Digital product.