IOPS with RAID Penalty
Define the disks, RAID level and read/write mix and I compute the functional IOPS applying the write penalty (RAID5=4, RAID6=6, RAID1/10=2) over the raw IOPS.
Disk I/O split
At the operating point, the array's physical I/O (—)
splits between reads and writes; each application write costs
— disk I/O.
The same workload on other RAID levels
| RAID | Penalty | Functional IOPS | Backend W |
|---|
With 8 disks of 180 IOPS and
70% read.
How it is computed · IOPS and the write penalty
Raw raw IOPS = number of disks × IOPS per disk. It is the physical ceiling of the array (all I/O to the backend).
Penalty each application write triggers several disk I/Os: RAID 0 = 1, RAID 1/10 = 2, RAID 5 = 4, RAID 6 = 6.
Functional functional IOPS = raw ÷ (read fraction + write fraction × penalty). These are the IOPS the application sees with that workload mix.
Backend W disk I/O from writes = functional IOPS × write fraction × penalty. Added to the reads it equals the raw IOPS.
Array-sizing model: it estimates how many disks you need for a workload at a given write percentage. The per-disk IOPS are reference values; measure your own for exact figures.
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