IOPS

Any storage performance are ultimately calculated by how best the underlying disks are performing.

IOPS is still the most common metric in use to measure the storage systems performance


IOPS calculations vary wildly based on the kind of workload being handled.

In general, there are three performance categories related to IOPS:
random performance, sequential performance, and a combination of the two,

which is measured when you assess random and sequential performance at the same time

IOPS is based on three key factors:
Rotational/spindle speed (A higher rotational speed is associated with a higher performing disk.)

Average Latency (time it takes for the sector of the disk being accessed to rotate into position under a read/write head.)

Average seek time (time (in ms) it takes for the hard drive's read/write head to position itself over the track being read or written. There are both read and write seek times; take the average of the two values)

Average IOPS Formula:
Divide 1 by the sum of the average latency in ms and the average seek time in ms
(1 / (average latency in ms + average seek time in ms).

3ms   = average latency time
4.2ms = average seek time (read/write)

1/ 3ms + 4.2ms
1/7.2ms
1/.0072 = 138.88 = 139 IOPS


Average IOPS
SATA 7200K - 75-100
SATA 10K - 125-150
SAS 10K - 140
SAS 15K - 175-210
FC 15K - 200


Enterprises don't install a single disk at a time,
so the above calculations are pretty meaningless unless they can be translated to multidisk sets.
Fortunately, it's easy to translate raw IOPS values from single disk to multiple disk implementations;

For example, if you have ten 15K RPM disks, each with 175 IOPS capability, your disk system has 1,750 IOPS worth of performance capacity.
But this is only if you opted for a RAID-0 or just a bunch of disks (JBOD) implementation.