IOSIM(1)

💖 NAME 💖

okay so bestie, welcome to iosim(1) from the General Commands Manual — a performance tool to simulate I/O workloads. literally it's giving “let’s fake some I/O and watch the numbers,” and honestly? iconic. 💅

🦋 SYNOPSIS 🦋

here’s the whole flag lineup, no cap. every default and valid range is exactly as written, so don’t come for me:

• -c <number> — Burst Count. No. of I/Os performed in an I/O burst. Default Value: 10; Valid Range: [0, INT_MAX]
• -i <msecs> — Inter Burst Duration. Amount of time each thread sleeps between bursts (-1 indicates random durations between 0-100 msecs). Default Value: 0; Valid Range: [-1, INT_MAX]
• -d <msecs> — Inter I/O delay. Amount of time thread sleeps between issuing I/Os. Default Value: 0; Valid Range: [0, INT_MAX]
• -t <number> — Thread count. Default Value: 1; Valid Range: [0, 1000]
• -f <number> — Workload Type (0/1/2 : Read-Only/Write-Only/Mixed RW). Default Value: 0; Valid Range: [0, 2]
• -m <number> — I/O Pattern (0/1 : Sequential/Random). Default Value: 0; Valid Range: [0, 1]
• -j <bytes> — Size of I/O in bytes. Default Value: 4096; Valid Range: [0, INT_MAX]
• -s <msecs> — Frequency of sync(2) calls. Default Value: 5000; Valid Range: [0, INT_MAX]
• -l <number> — I/O Tier (0/1/2/3). Default Value: 0; Valid Range: [0, 3]
• -z <number> — Size of the file created specified in pages (Only used when the file is being created by the tool). Default Value: 1 GB; Valid Range: [0, INT_MAX]
• -x <secs> — Test duration (0 indicates that the tool would wait for a Ctrl+C). Default Value: 0; Valid Range: [0, INT_MAX]
• -a number — I/O Caching behavior (0/1 : Non-cached/Cached). Default Value: 0; Valid Range: [0, 1]
• -n <filename> — Filename for I/Os (If this option is not specified, the tool would create files on its own). Valid Range: Valid filename

💜 DESCRIPTION 💜

okay so iosim is the performance tool for simulating I/O workloads, specifically so you can evaluate I/O performance. It spawns n threads that issue non-cached I/Os. If specified, it also creates a sync thread that issues system-wide sync(2) calls to flush data and metadata to disk — yes, it emulates launchd behavior. The I/Os are issued at the specified I/O tier, and the tool reports latency and throughput numbers. 🫶

and here’s the results decoder ring, bestie:

• Avg. Latency — the average latency experienced by the I/Os.
• Low Latency Histogram — frequency distribution of I/O latency for low latency I/Os.
• Latency Histogram — frequency distribution of I/O latency.
• Burst Avg. Latency Histogram — frequency distribution of burst avg. latency.
• Throughput timeline — time windowed throughput distrbution (keeping that spelling exactly as it is, bestie 😭).

🎀 SEE ALSO 🎀

• fs_usage(1) — go give her a look too, iykyk.

this iconic page is from macOS, dated October 9, 2013, and the source/version footer says IOSIM(1). mwah 💋✨