Benchmark: md_raid5 – comparing 4 hard drives versus 3

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lrg tango drive hard disk Benchmark: md raid5   comparing 4 hard drives versus 3Recently i had to grow the capacity of my NAS. The NAS is running Debian and RAID is powered by md. I had attached 3 hard drives to it which were working as RAID5 array. Now i could write about how to grow a RAID, but you will be able to read that on more than enough other websites. I would rather share a benchmark i have created using Bonnie++. Let me show you the effects of changing the amount of hard drive on the read and write performance.

The theory is that the more hard drives are in an array the more performance in reading and writing you will have. But having more hard drives will mean that the parities have to be distributed complexer what would reduce to write performance.

According to my benchmark these facts have been proven because i could notice an enhancement on reading and writing throughput. Have a look at the diagrams:

Anzahl Platten Sequential Output
Per Chr
K/sec %CP
4 551 97
3 540 97
Block
K/sec %CP
4 94653 18
3 56140 10
Rewrite
K/sec %CP
4 61931 10
3 33581 5
Sequential Input
Per Chr
K/sec %CP
4 1841 92
3 1898 94
Block
K/sec %CP
4 225288 15
3 121653 8
Random
Seeks
Seeks/sec %CP
4 250,1 5
3 206,1 4

md raid5 bench3vs4disks html opc 234x300 Benchmark: md raid5   comparing 4 hard drives versus 3md raid5 bench3vs4disks html ipc 234x300 Benchmark: md raid5   comparing 4 hard drives versus 3

Per Char there are no logical changes. The fact that the proportion has turned might be an accident.

md raid5 bench3vs4disks html ob 234x300 Benchmark: md raid5   comparing 4 hard drives versus 3md raid5 bench3vs4disks html ib 238x300 Benchmark: md raid5   comparing 4 hard drives versus 3

The bars rise sensible here

md raid5 bench3vs4disks html rewrite 234x300 Benchmark: md raid5   comparing 4 hard drives versus 3md raid5 bench3vs4disks html seeks 234x300 Benchmark: md raid5   comparing 4 hard drives versus 3

On Rewrite the factor x2 can be noticed and the Random Seeks are 40-50 more per second.

Altogether you can say that the performance of the RAID has really increased a lot after attaching one more hard drive. With an input of 225.288 K/s i have exceeded the theoretical speed of Gigabit Ethernet (120 MB/s) obviously.

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