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Disk IOPS From Spindles Calculator

Work out disk iops from spindles instantly with clear inputs, formula shown and shareable results.

About Disk IOPS From Spindles Calculator

Each host write becomes several back-end operations under parity RAID: RAID 5 needs two reads and two writes, giving a penalty of 4, and RAID 6 a penalty of 6. Front-end IOPS is therefore raw IOPS divided by the read-weighted average penalty, which is why a write-heavy workload on RAID 6 delivers a fraction of the array's nominal capability.

Formula

RAID IOPS

raw = disks x per-disk IOPS; effective = raw / (read share + write share x write penalty)

Worked example

With the default values below, Disk IOPS From Spindles Calculator returns Effective front-end IOPS of 1,292. Change any input above and every figure here is recalculated in your browser.

Inputs used

Disks in the arrayminimum 1
12
Disk typeone of 7200 rpm SATA (~80 IOPS), 10k rpm SAS (~140 IOPS), 15k rpm SAS (~180 IOPS), SATA SSD (~20,000 IOPS)
10k rpm SAS (~140 IOPS)
RAID levelone of RAID 0 - no penalty, RAID 1 or 10 - write penalty 2, RAID 5 - write penalty 4, RAID 6 - write penalty 6
RAID 1 or 10 - write penalty 2
Read share of the workloadaccepts 0–100 %
70 %

Results

Effective front-end IOPS
1,292 IOPS
Raw back-end IOPS
1,680 IOPS
RAID write penalty
2 x
Write IOPS available
388 IOPS

Step by step

  1. 1Values used
  2. 2RAID IOPS
  3. 3Effective front-end IOPS= 1,292 IOPS
  4. 4Raw back-end IOPS= 1,680 IOPS
  5. 5RAID write penalty= 2 x
  6. 6Write IOPS available= 388 IOPS

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Where does the RAID 5 penalty of 4 come from?

A partial-stripe write reads the old data and old parity, then writes the new data and new parity — four operations for one logical write.

Do SSDs have the same penalty?

The RAID arithmetic is identical, but their IOPS ceiling is so much higher that the penalty rarely binds. SSD write amplification and endurance become the concern instead.

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