Disk IOPS & Throughput
IOPS ↔ throughput at a block size, IOPS from queue depth and latency (Little’s law), and functional IOPS of a RAID set from write penalty and read/write mix.
Throughput in MiB/s and MB/s, IOPS, the implied queue depth or latency, and for an array the raw and functional IOPS after the RAID write penalty — per-disk figures are yours.
Example: 10,000 IOPS at 4 KiB is 39.1 MiB/s; at 1 ms latency that needs a queue depth of 10. Eight such disks in RAID 5 at 70 % reads give 42,105 functional IOPS from 80,000 raw (write penalty 4).
Three identities
and a write penalty.
How IOPS, block size, throughput, queue depth and latency relate, and where the RAID penalties come from.
IOPS and throughput
Throughput = IOPS × block size, so 10,000 IOPS of 4 KiB I/O is 39 MiB/s while 4,000 IOPS of 128 KiB is 500 MiB/s — an IOPS figure means nothing without its block size. The reverse divides throughput by block size. MiB/s (2²⁰) and MB/s (10⁶) are both shown.
Little’s law
For a queue in steady state, throughput × latency = items in the system: IOPS = queue depth ÷ latency. Thirty-two outstanding I/Os at 0.5 ms each is 64,000 IOPS; and when you enter IOPS and latency the page reports the queue depth that implies, or the latency a queue depth implies.
RAID
Each RAID level’s write cost follows from its algorithm: RAID 0 writes once; RAID 1 and 10 write to both mirrors (2); RAID 5 reads the old data and parity, then writes new data and parity (4); RAID 6 does the same with two parities (6). Functional IOPS = raw ÷ (read share + write share × penalty). Per-disk IOPS is the figure you enter and is treated as equal for reads and writes; caches, parity logs and SSD write amplification move the real number. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- throughput = IOPS × block size; Little’s law IOPS = queue depth ÷ latency; functional IOPS = raw ÷ (reads + writes × penalty), penalties from the RAID algorithms: 1 (RAID 0), 2 (1/10), 4 (5), 6 (6)
Last reviewed 21 September 2026. How results are checked: How we verify.