Recently 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 Char there are no logical changes. The fact that the proportion has turned might be an accident.
The bars rise sensible here
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.