Well, now both Seagate and HGST/WD have released 6TB drives. What does that mean to the storage suppliers?
We all know that RAID rebuild time with RAID-6 and 8+2 can take days, depending on a number of factors. But add 50% to the density and it’s almost a surety that if I/O is going on from applications, it is going to take days to rebuild. Seagate publishes drive specifications that show 216 MB/sec or 205 MiB/sec, which the Seagate states is maximum sustained transfer rate.
Usually the average is in the manual, but it’s not available yet online. So my guess is the average transfer rate, based on historical data, is around 175 MB/sec. Let’s first assume best case, that is, maximum performance. That means that for a 6TB drive it will take 27,778 seconds (or about 7.7 hours), and using my best guess we could assume 9.5 hours.
This of course assumes no one is doing anything else but rebuilding. No user I/O, no system I/O, no disk scrubbing, nothing else. My guess based on today’s 4TB rebuilds is that we are talking best case rebuilding in 2.5 days on reasonable load, and under heavy load maybe as much as 4 days.
This of course is why I do not think RAID methods such as standard RAID-6 are going to work for large scale for drives at this size. The specifications for hard error rate did not change and we had another 50% increase in density. Consumers of enterprise storage are going to need to band together and demand that vendors use or develop new methods that address device failure and allow the system to operate at reasonable performance and high reliability. This will require all of us to make these demands.
