There’s no online capacity expansion in the FiT500, so changing the 2 disk RAID 0 to a 3 disk RAID 0 requires deleting the old array and creating the new array. Luckily the process takes only a minute or so to complete (so yes, theoretically, you could delete 8TB of data in just a few seconds if you had physical access to the device).
With a three disk RAID 0 array, ATTO shows us:
Interestingly the 3 disk array does not start out faster than the 2 disk array – indeed it does not pull ahead until the 8.0KB transfer test. After that though the 3 disk array accelerates up to 230MBps, where we seem to reach a different bottleneck. The eSATA interface should be good for 300MBps, so we're seeing only about 75% of maximum. Perhaps the 3 disks can only push 75MBps each - it's still a good result.
Let’s see what HDTach has to say about the 3 disk RAID 0 set:
Impressive. 200+MBps across the first 85% of the array. It seems clear that we are reaching a limit of the embedded RAID controller chip at these throughputs - if not, then we'd expect the graph to be higher at the start and decrease over the entire range. Time for HD Tune then, to see the difference between sequential and random access:
An average of 190MBps across the array makes this no slouch. It matches up with HDTach, although at a slightly lower level (perhaps due to different methods of performing IO).
Again, though, the result of ~50 IOPS is about what we’d expect to see from a single disk, so like the 2 disk array, there is no real benefit to random IO. It looks like the extra latency of the embedded RAID controller is too great to achieve high random IO rates.
