HPE Storage Users Group

I'm putting in a small 7200 with 16 - 300GB 15k drives. With the small capacity of this unit, I was thinking it would be best to optimize space over speed and do RAID 5 7+1 vs 3+1? How would I find the optimal setting so that the drives are loaded evenly?

According to the NinjaSTARS tool they are identical other than space available.

Both give a max of 2,001 IOPS (based on a 50:50 r/w ratio) @ 15ms response rate (QD=30), with between 2.6 and 3.0TB of space usable. The numbers aren't any different for 2, 3 or 4 shelves either so its entirely based on number of disks.

Adding 8 x 100GB SSD's pushes these numbers upto a peak throughput of 54,000 IOPS and a realistic of between 13.3K (3+1) and 11.1K (7+1) @ 2.6-3.03ms - realistic presumes a lot of requests can be serviced from SSD (e.g. small heavily used data areas or AO optimisation of hot data).

Increasing the r/w hit ratio pushes things up too - with 70:30 r/w the 54K figure goes to 70K and the 13.3K goes to 15.8K and the 11.1K to 13.2K. Wthout the SSD, increasing the r/w to 70:30 puts the IOPS up from 2K to 2.3K or so.

So its only when there are more disks or if there is more than one type of disk that things change.

Cool, then I think I'll optimize my available space at go for the R5 7+1. I think based on some math the optimal growth size should be 14GB (16 drives * 7 data / 8 set size).