Performance in Intel IOMeter
This pattern sends a stream of requests to read and write 8KB random-address data blocks. By changing the ratio of reads to writes we can check how well the controller’s driver can sort them out. The results of the controller in WriteBack mode are presented below, however, for your convenience we have split them in three groups:
Let’s take a look at the graphs which will show the dependence of the controller’s speed on the percentage of write requests for queues of different depths. All the graphs have been arranged in groups depending on the queue depth:
All the arrays perform very close to one another under linear workload (RandomRead mode in the beginning of the graph), because the array algorithms have nothing to optimize.
As the probability of write increases, the performance of a single HDD grows up gradually: the HDD lazy write algorithms kick in. The performance of RAID0 array increases together with the growing number of drives in the array, however, this growth is proportional only in case of the highest write probability.
The performance of RAID5 arrays should drop down as the probability of writes increases, however, we see a completely different picture. The behavior of RAID5 array graphs is very similar to what we saw with RAID0 and is most likely to be determined by the dominating lazy write algorithms of the HDDs. Nevertheless, when there are few drives in the array and the probability of writes is relatively high, the RAID5 arrays speed decreases as the writes probability grows up.
RAID1 mirrored array disappointed us: it appeared slower than the single HDD in almost all modes. It was a pretty unexpected result, because all 3ware controllers use their brand name Twinstor technology to speed up reading from mirrored arrays. This technology uses the previous requests history to determine the HDD that will process the current request faster, thus speeding up the entire array. And as we have seen from our previous experiences with 3ware controllers, Twinstor technology has always had a positive effect. Hopefully, this algorithm will start working properly under higher loads.
The performance graphs of another mirrored array – RAID10 – just like the graphs for RAID0 and RAID5, show mostly the influence of the HDD lazy writing algorithms.