Performance in Intel IOMeter DataBase Pattern
So, we are sending a mixed stream of requests for reading and writing 8KB data blocks with a random address. By changing the ratio of reads/writes we can estimate how good the controller driver is at sorting such requests out.
The results of the controller in the WriteBack mode are listed below:
Let’s view the numbers as diagrams. The diagrams show the dependence of the data-transfer rate on the percent of writes among the requests. We will take the measurements for the queue being 1, 16 and 256 requests long. For better readability, we split the arrays into two groups:
Under the linear workload, in the random read mode, all arrays show similar performance. It is natural for RAID0, RAID5 and JBOD arrays to behave this way in this mode, but it also means that there is no requests alternation between the disks of a mirror couple on RAID1 and RAID10 arrays.
As there are more write requests in the queue, the disks can perform lazy writing more efficiently and the single disk as well as the arrays gains its speed. The performance of the RAID0 array grows in proportion to the number of drives in the array, but only due to the lazy write algorithms enabled on the disks.
The graph for RAID1 array nearly coincides with the graph for the single drive, which is indicative of the absence of a requests alternation algorithm. The graph of the second array with mirror couples –RAID10 – is less “smooth”. However, as the mirror couples are joined into RAID0 arrays here, the speed of the RAID10 under this workload is very close to that of the two-disk RAID0.
The performance of the RAID5 array should be getting lower as the writes percentage increases, since write requests slow this type of array down considerably. In our case, however, the arrays even increase their speed in some operational modes. This is probably due to the fact that each write operation actually produces two write requests for RAID5 arrays and increases the average drive workload. In such circumstances, the efficiency of the drive’s lazy write increases.