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Performance in Intel IOMeter

Sequential Read & Write Patterns

This time we would like to start the discussion of test results with the sequential patterns for pretty obvious reasons. In these patterns the storage devices receive a chain of requests with queue depth of 4. Once a minute the data block size increases. As a result, we can check the dependence of array linear read and write speeds on the size of the data block and this way estimate maximum achieved speed.

There is almost no difference between the two test cycles. It fits within the measurement accuracy range. The order of test loads has no effect on sequential reading. What can we see in the diagram? First, the 2-level RAID10 and RAID50 arrays are somewhat slower than the other arrays on small data blocks. Second, the controller is obviously trying to read data from both disks in mirror pairs, but only on large data blocks. The top speeds are all right. You can predict them by knowing the speed of the single disk and making allowances for a minor loss of efficiency. It is only sad that the arrays reach those top speeds on rather large data blocks. We have seen higher speeds in our comparative review.

After this diagram we could give out a sigh of relief because we had managed to make the controller deliver a decent speed of writing. The results of the first cycle are somewhere at the bottom of the diagram whereas the second-cycle speeds are much better, even though not perfect. The RAID5 and RAID50 stumble on medium-size data blocks for some reason. The RAID10’s flat stretch on 16 to 32KB blocks is no good, either. On very large data blocks the top speeds are proper enough: the RAID0 is almost as fast as 1000MBps. The RAID5 is slower by the speed of one disk. The RAID6 and RAID50 are slower yet because they have two disks for writing checksums to. The RAID10 is almost exactly half as fast as the leader.

 
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