Work out iops requirement instantly with clear inputs, formula shown and shareable results.
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.
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
Because durability requires the write to reach persistent storage. Write-back caching can batch and coalesce writes but cannot eliminate them.
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.