A four disk RAID 3 array can be problematic. Writing a large amount of data (more than a stripe) may require that the blocks of data, which are generally sized as a power of 2, be broken into an odd number of equal chunks so that it can be stored, and the parity information calculated.
So what can ATTO show us about a four disk RAID 3 array:
Performance is pretty good, on par with the 3 disk RAID 0 array. There doesn't appear to be any significant issue for this RAID controller in dealing with large chunks of data; an excellent outcome. Let’s see what HDTach has to say about the 4 disk RAID 3 set:
Impressive. 200+MBps sustained across the first 85% of the array, just like the 3 disk RAID 0 array - they're indistinguisable it seems. It also seems clear that the limit of the embedded RAID controller chip is more about throughput than parity calculations. HDTune then, to see the difference between sequential and random access:
There are a couple of minor dips in performance, but nothing particularly troubling. We match the sequential performance curve from HDTach.
Random performance of the RAID 3 set. There is nothing insightful to say here.
