As the workload increases, we see the arrays perform at different speeds. The “mirror” arrays run much faster when the reads share is high, but lose their speed as the share of writes increases. These arrays are efficient at reading random-address data due to TwinStor technology. Ideally, you get a double performance gain in reading speed.
Anyway, RAID1 is always faster than the single drive, while RAID10 is in its turn faster than the two-drive RAID0 across all the operational modes. RAID0 arrays should actually be the fastest, but as we explained in our previous review, random selection of the drive to read from may lead to a situation when some drives are overloaded and the others stay idle. Meanwhile, “mirror” arrays alternate requests between the disks (basing on the access statistics), thus creating the same or similar workload for all drives in the array. That’s why when the writes share is low (below 30%), RAID1 outperforms even RAID0 of two disks, while RAID10 outperforms RAID0 arrays of three and four disks when the writes share is below 40% and 20%, respectively.
Of course, we couldn’t pass by the small slump in performance RAID0 arrays of three and four drives suffered on 10% writes. As you remember, we saw a similar slump with Intel SRCS14L and Promise FT S150 TX4 controllers. It seems like 3ware 8500-8 controller takes some time to execute the lazy write algorithm, and the resulting optimization doesn’t compensate for that time when there are only 10% of write requests.
The graphs for RAID0 arrays have the same shape as the graph for the single drive, indicating that the StorSwitch architecture shows excellent results at sorting requests out and sending them to the appropriate hard disk. On the other hand, we still see the slumps in performance of the RAID0 arrays of three and four drives on 10% writes. The influence of TwinStor on “mirror” arrays, RAID1 and RAID10, is the highest in the Random Read mode and when there are enough requests in the queue, so these arrays are doing faster than RAID0 arrays of two and four disks, respectively.