# fio — Flexible I/O Tester for Storage Benchmarking

> fio is a configurable I/O workload generator used to benchmark and stress-test storage subsystems with precise control over read/write patterns, block sizes, and concurrency.

## Install

Save as a script file and run:

# fio — Flexible I/O Tester for Storage Benchmarking

## Quick Use
```bash
# Install
apt install fio   # or: brew install fio / dnf install fio

# Random 4K read benchmark, 4 jobs, 30 seconds
fio --name=rand-read --ioengine=libaio --rw=randread --bs=4k 
    --numjobs=4 --size=1G --runtime=30 --time_based --group_reporting

# Sequential write throughput test
fio --name=seq-write --ioengine=libaio --rw=write --bs=1M 
    --numjobs=1 --size=4G --direct=1 --group_reporting
```

## Introduction
fio (Flexible I/O Tester) is the industry-standard tool for benchmarking storage devices and filesystems. Written in C, it can simulate virtually any I/O workload pattern by combining configurable block sizes, queue depths, access patterns, and I/O engines. It is used by storage vendors, kernel developers, and DevOps engineers to validate hardware and tune systems.

## What fio Does
- Generates sequential, random, or mixed read/write workloads at any block size
- Supports dozens of I/O engines including libaio, io_uring, sync, mmap, and RDMA
- Runs multiple parallel jobs to stress-test concurrency and queue depth scaling
- Reports IOPS, bandwidth, and latency at configurable percentile levels
- Accepts job files in INI format for repeatable, shareable benchmark definitions

## Architecture Overview
fio spawns one or more worker threads or processes, each executing an I/O loop defined by a job specification. Each job selects an I/O engine (the syscall or library interface), an access pattern (sequential, random, zipf), and parameters like block size and queue depth. A central statistics collector aggregates per-job metrics and emits a summary with IOPS, bandwidth, and latency percentiles.

## Self-Hosting & Configuration
- Install via package manager or compile from source with `./configure && make`
- Define workloads in `.fio` job files (INI-style) for reproducible benchmarks
- Use `--direct=1` to bypass the page cache and measure raw device performance
- Select the I/O engine matching your target: `io_uring` for modern Linux, `libaio` for legacy
- Output results as JSON with `--output-format=json` for automated analysis pipelines

## Key Features
- Supports 30+ I/O engines including io_uring, libaio, POSIX AIO, and Windows IOCP
- Configurable access patterns: sequential, random, strided, and custom distributions
- Per-job and group reporting with latency histograms and percentile breakdowns
- Verification mode writes checksums and reads them back to detect data corruption
- Job file format allows sharing and version-controlling benchmark definitions

## Comparison with Similar Tools
- **sysbench fileio** — Simpler file I/O test but far fewer tuning options than fio
- **dd** — Basic sequential throughput test, no random I/O or latency reporting
- **bonnie++** — Classic filesystem benchmark with fixed test patterns
- **Iometer** — Windows-centric GUI benchmark, less flexible than fio on Linux
- **diskspd** — Microsoft's storage benchmarking tool, Windows-focused

## FAQ
**Q: Should I use direct I/O or buffered I/O for benchmarks?**
A: Use `--direct=1` to measure raw device speed. Buffered I/O benchmarks test the page cache, which is useful for application-level analysis.

**Q: What I/O engine should I use on modern Linux?**
A: `io_uring` offers the best performance on Linux 5.1+. Fall back to `libaio` for older kernels.

**Q: How do I benchmark NVMe devices?**
A: Use `io_uring` or `libaio` with high `iodepth` (64-256) and multiple jobs to saturate the device's internal parallelism.

**Q: Can fio simulate real application workloads?**
A: Yes. Record an application's I/O trace with blktrace and replay it with fio's `replay_redirect` option.

## Sources
- https://github.com/axboe/fio
- https://fio.readthedocs.io/

---
Source: https://tokrepo.com/en/workflows/asset-94698b64
Author: Script Depot