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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 the array’s sequential read/write speed on the size of the data block. This test is indicative of the highest speed the array can achieve.

We’ve got a nearly ideal picture of maximum speeds at reading. The RAID5 arrays with N disks are as fast as the RAID0 arrays with N-1 disks. The mirrored arrays with 2*N disks are exactly as fast as RAID0 arrays with N disks (e.g. the two-disk RAID1 equals the single disk). You can see a characteristic thing with the mirrored arrays: their speed grows up somewhat on very large data chunks because the controller begins to read data from both disks of each mirror.

Note also that the many-disk arrays only show their advantage with 8KB and larger blocks. With smaller data blocks the arrays differ but slightly.

Sequential writing is just as good as sequential reading: everything works well. We don’t see any negative influence of the controller’s algorithms. That’s an excellent result that doesn’t need any comments.

 
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