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Sequential Read & Write Patterns

IOMeter is sending a stream of read and write requests with a request queue depth of 4. The size of the requested data block is changed each minute, so that we could see the dependence of an array’s sequential read/write speed on the size of the data block. This test is indicative of the highest speed a disk array can achieve.

The 8-disk RAID0 is almost as fast as 1000MBps on large data blocks, which is an excellent result. The scalability is all right, too. The controller even tries to read from both disks in the mirror pairs on very large data blocks, but the performance growth is not big. The degraded RAID10 passes this test almost without any loss of speed.

The checksum-based arrays cope with reading well: their speeds are just what you can expect if you know the speed of the single HDD. The degraded arrays are surprisingly slow here: the controller is not quite good at restoring data from checksums.

We see inexplicable fluctuations of speed of every array at writing. The 8-disk RAID0 does not reach its theoretical speed. The 4-disk RAID10 and RAID0 have problems with medium-sized and large data chunks, respectively. The top speed of the 8-disk RAID0 is good, but it is the slowest of all on small data blocks and we have no explanation for that.

The RAID5 and RAID6 arrays have problems with writing, too. There are flaws in the controller’s firmware. This is the only explanation why the degraded arrays are superior to the healthy ones. The 8-disk RAID6 is too slow on large data blocks.

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