Enterprise SATA/SAS 4 TB drives are here, in case you had not seen. I am sure that RAID vendors will be soon qualifying the drives, and we will see them in storage controllers in a few months or less, as some vendors might have already started qualification. I have a concern that RAID-6 is not robust enough to deal with the density, given the long rebuild times and the potential for a triple failure. I wrote about this about 2.5 years ago, and I have seen little movement in the industry to support declustered RAID across the industry. I would not be purchasing 4 TB drives from any vendor unless that vendor supported some type of declustering algorithm, as rebuild times with 4 TB drives will increase the likelihood for a triple failure with RAID-6. Do not even consider RAID-5. Of course, you could go to RAID-6 4+2 to reduce the impact, but you are now using 12 drives vs. 10 drives. It kind of defeats the purpose, doesn't it?
If I were purchasing storage, I would either demand that the vendor provide declustered RAID support or say that I will buy its product with only 2 TB drives. Those vendors that support declustered RAID will have a major price advantage. The Hitachi data was not clear on the performance -- it said 171 MB/sec sustained rate. I am not sure if that is 1024*1024 or 1000*1000 and if the 171 is sustained for the whole drive or just a portion of the drive. Anyway, using 1024 and 171 MB/sec for the whole drive (just a guess) it takes more than 6 hours to read the whole drive. That, of course, assumes you are doing nothing else. We as customers need to demand 4 TB drives with declustered RAID.