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IOPS Requirement Calculator

Work out iops requirement instantly with clear inputs, formula shown and shareable results.

About IOPS Requirement Calculator

Application I/O is not storage I/O. Reads that hit the buffer pool never reach the device, so an 85 percent cache hit rate removes most of the read load while every write must still be persisted. Provisioning on logical IOPS overspends enormously; provisioning on physical IOPS with 30 percent headroom is the realistic figure.

Formula

Physical IOPS

logical = TPS x I/O per transaction; physical = logical x read share x (1 - cache hit) + logical x write share; provision at 1.3x

Worked example

With the default values below, IOPS Requirement Calculator returns IOPS to provision including headroom of 5,655. Change any input above and every figure here is recalculated in your browser.

Inputs used

Transactions per secondminimum 0.001
2,000
I/O operations per transactionminimum 0.01
6
Read share of I/Oaccepts 0–100 %
75 %
Cache hit rate on readsaccepts 0–100 %
85 %

Results

IOPS to provision including headroom
5,655 IOPS
Physical IOPS reaching storage
4,350 IOPS
Logical IOPS from the application
12,000 IOPS
Read IOPS absorbed by cache
7,650 IOPS

Step by step

  1. 1Values used
  2. 2Physical IOPS
  3. 3IOPS to provision including headroom= 5,655 IOPS
  4. 4Physical IOPS reaching storage= 4,350 IOPS
  5. 5Logical IOPS from the application= 12,000 IOPS
  6. 6Read IOPS absorbed by cache= 7,650 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, 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 the write share not benefit from cache?

Because durability requires the write to reach persistent storage. Write-back caching can batch and coalesce writes but cannot eliminate them.

Should IOPS or throughput be provisioned?

Whichever binds. Small random I/O is IOPS-bound; large sequential I/O is throughput-bound. Cloud volume types have separate limits for each and both must be checked.

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