RAID Performance Calculator
Estimate combined read and write IOPS across a RAID array based on level and disk count.
About RAID Performance Calculator
RAID write penalties reflect the extra I/O operations required per logical write: RAID 0 has no penalty (1:1), RAID 1/10 must write to both mirrors (2:1), RAID 5 must read old data + old parity + write new data + write new parity (4:1), and RAID 6 adds a second parity update (6:1). Effective IOPS is calculated by dividing the total raw IOPS by the weighted average of read and write penalties based on the workload's read/write ratio.
Formula
Effective IOPS
effective_IOPS = (n × disk_IOPS) / (read% + write% × write_penalty)
- n
- disk count
- I_{disk}
- IOPS per disk
- r
- read fraction
- w
- write fraction
- P_w
- write penalty factor
Worked example
With the default values below, RAID Performance Calculator returns Effective IOPS of 632. Change any input above and every figure here is recalculated in your browser.
Inputs used
- RAID Levelone of RAID 0, RAID 1, RAID 5, RAID 6, RAID 10
- RAID 5
- Number of Disksminimum 2
- 6
- Single Disk IOPSminimum 1
- 200
- Read Percentageaccepts 0–100 %
- 70 %
Results
- Effective IOPS
- 632
- Effective Read IOPS
- 442
- Effective Write IOPS
- 189
- Write Penalty Factor
- 4
- Total Raw IOPS
- 1,200
Step by step
- 1Total raw IOPS= 1200
- 2Write penalty for RAID 5= 4x
- 3Effective IOPS= 632
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, fees or charges 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
Why does RAID 5 have a write penalty of 4?
Each logical write requires reading the old data stripe, reading the old parity stripe, writing the new data stripe, and writing the recalculated parity stripe — 4 physical I/O operations total.
How does read/write ratio affect performance?
Higher read percentages improve effective IOPS because reads have no penalty (1:1), while writes multiply the load by the penalty factor — a 90% read workload on RAID 5 performs much closer to raw disk IOPS than a 50/50 workload.