The better your controller, the better it scales. In our testing, the Areca ARC-1220 is capable of benefiting from multiple hard drives in RAID 5 or RAID 6 setups. A single HD321KJ from Samsung provides up to 82 MB/s. A RAID 5 with three hard drives corresponds to a RAID 0 array with two hard drives, which is why a three-drive setup practically doubles the performance of a single drive. Adding more hard drives adds considerably more throughput with each additional drive, but the test system starts to max out with six hard drives, reaching 356 MB/s. Eight drives will only give you slightly more performance, with a data transfer rate of 384 MB/s.
Write Transfer Rates
Parity calculation takes time. This becomes very obvious when looking at the write performance results. While read transfer rates of almost 400 MB/s were possible, RAID 5 setups with multiple drives did not even achieve half of that. For RAID 6 setups, the maximum write transfer rates were less than 150 MB/s with eight hard drives. It is, however, very interesting to see that the minimum transfer rates clearly benefit from a higher drive count, although the maximum value doesn’t differ much between three and eight drives (RAID 5). Clearly, the controller cannot process more XOR data.