optimal-io-size · shipping · also optimal_io_size, OPT-IO, io_opt

Optimal I/O size

Optimal I/O size is a Linux block-layer hint for the preferred request unit for sustained I/O, expressed in bytes.

Zero means no optimum was reported, not that zero-length requests are useful. Treat the value as a workload starting point, not a measured best size for every application. [1]

Relations

related

Minimum I/O size, Alignment offset, Partition alignment, Physical sector

Advantages

• The blockdev --getioopt query can record the hint without issuing a data write. [2]

Limitations

• For partitions, lsblk can inherit queue attributes from the parent, so matching rows are not independent device measurements. [3]

Citations

1. Linux 6.12: stable sysfs block ABI, sector sizes and I/O topology (accessed 2026-10-19)
2. util-linux 2.40.2: blockdev query options and byte units (accessed 2026-10-19)
3. util-linux 2.40.2: lsblk explicit columns and inherited queue attributes (accessed 2026-10-19)

Further reading

4. Hesela: 512e, 4Kn and alignment: geometry is not durability (accessed 2026-10-19)

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