io-request-size · shipping · also Benchmark block size

I/O request size

I/O request size is the number of bytes requested by one input/output operation at a specified system boundary.

fio's blocksize configures bytes per I/O; bssplit permits a mixture of sizes [1]. This is distinct from a device's logical sector or filesystem allocation unit. Kernel request merging can change counts and sizes below the application boundary [2]. When relating successful data-transfer IOPS to bytes/s, use the actual completed bytes and matching operation population, especially if sizes vary or transfers are short [3].

Relations

related

iops, throughput-storage, queue-depth, logical-sector, physical-sector, partition-alignment

Limitations

• Equal IOPS at different request sizes does not imply equal data throughput; a byte-weighted size average is not the required operation-weighted mean. [3]

Citations

1. fio documentation: blocksize, bssplit, I/O depth and interpreting the output; online manual reviewed 13 October 2026. (accessed 2026-10-13)
2. Linux kernel documentation: I/O statistics fields; completed requests, merged requests and sectors. (accessed 2026-10-13)
3. Hesela: IOPS, bytes and average occupancy; synthetic accounting examples. (accessed 2026-10-13)

JSON: /data/terms/io-request-size.json