Estimate combined read and write IOPS across a RAID array based on level and disk count.
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.
Effective IOPS
effective_IOPS = (n × disk_IOPS) / (read% + write% × write_penalty)
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.
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.