Quest for Speed, part 1

In a new series involving our neverending quest for increased metaverse performance I've begun gathering additional data and metrics to help predict performance for the MIIS database. See the original post - "MIIS Database Sizing - Learning from Exchange" for information regarding the I/O calculations.

Fine Tuning the IOPS for Rotational Speed

So, in a previous posting we talked about some recommended constants regarding the number of I/O operations per second (IOPS) based on rotational speed. We had the following table:

Rotational Speed	IOPS
7200 RPM	72
10,000 RPM	100
15,000 RPM	150

As it turns out, these are merely guidelines - if you want to fine tune these based on the actual specifications of your drive then you can use the following calculation I found here:

iops = 1000 (ms/s) / (average read seek time (ms) + (maximum rotational latency (ms) / 2))

Use the following table to lookup maximum rotational latency by rotational speed - we'll need this to fine tune our expected IOPS:

Rotational Speed	Max Rotational Latency
7200 RPM	8.3 ms
10,000 RPM	6 ms
15,000 RPM	4 ms

Now that we have this information we just need to find the Average Seek Time published for the drive type we're going to fill our array with. Referenced data is from HP's website:

	10k 3.5 U320 SCSI	15k 3.5 U320 SCSI	15k 3.5 SAS	15k 2.5 SAS
Avg Seek Time (across capacities)	5.4 ms	3.8 ms	3.5 ms	3.0 ms
Expected IOPS per spindle	119	172	182	200

So, as you can see that while the faster rotational speed does make a huge difference in performance, the move to the Small Form Factor (SFF) drives is also having the effect of speeding up the average seek times. To get an exact measurement you will want to find the exact specifications for your drive and use that in your calculations.