为什么需要fio？
在实际生产环境中，了解磁盘的 I/O 性能至关重要：
fio是什么？
fio 由 Jens Axboe（Linux 内核块层核心维护者）开发，是目前 Linux 生态中最强大、最灵活的磁盘 I/O 性能测试工具。它支持：
多种 I/O 类型：顺序/随机 读/写/读写混合
多种 I/O 引擎：sync、mmap、libaio、io_uring、posixaio、sg 等
精确的延迟统计：P50/P95/P99/P99.9 延迟分布
丰富的 workload 模拟：数据库、文件服务器、Web 服务器等
可编程 job file：支持多线程/多进程并发测试
多种输出格式：终端文本、JSON、JSON+、Terse 等
fio概念示意图
实际演示
fio的参数众多，这里通过一个具体的例子来展示。这条命令模拟数据库的使用情况，读写比是7/3。
fio --name=oltp-sim \ --ioengine=libaio \ --direct=1 \ --bs=8k \ --size=3G \ --rw=randrw \ --rwmixread=70 \ --iodepth=32 \ --numjobs=4 \ --group_reporting \ --runtime=120 \ --time_based \ --ramp_time=30
选项介绍：
命令执行完整输出：
oltp-sim: (g=0): rw=randrw, bs=(R) 8192B-8192B, (W) 8192B-8192B, (T) 8192B-8192B, ioengine=libaio, iodepth=32...fio-3.36Starting 4 processesoltp-sim: Laying out IO file (1 file / 3072MiB)oltp-sim: Laying out IO file (1 file / 3072MiB)oltp-sim: Laying out IO file (1 file / 3072MiB)oltp-sim: Laying out IO file (1 file / 3072MiB)Jobs: 4 (f=4): [m(4)][100.0%][r=161MiB/s,w=70.5MiB/s][r=20.6k,w=9026 IOPS][eta 00m:00s]oltp-sim: (groupid=0, jobs=4): err= 0: pid=54727: Thu Jun 25 09:23:16 2026 read: IOPS=38.7k, BW=302MiB/s (317MB/s)(35.4GiB/120002msec) slat (nsec): min=785, max=3517.1k, avg=5204.50, stdev=9422.74 clat (usec): min=55, max=201863, avg=2136.30, stdev=6055.59 lat (usec): min=153, max=201866, avg=2141.50, stdev=6055.62 clat percentiles (usec): | 1.00th=[ 685], 5.00th=[ 914], 10.00th=[ 1045], 20.00th=[ 1254], | 30.00th=[ 1450], 40.00th=[ 1696], 50.00th=[ 1893], 60.00th=[ 2057], | 70.00th=[ 2212], 80.00th=[ 2376], 90.00th=[ 2638], 95.00th=[ 2868], | 99.00th=[ 3490], 99.50th=[ 4146], 99.90th=[102237], 99.95th=[189793], | 99.99th=[200279] bw ( KiB/s): min=53589, max=374230, per=100.00%, avg=310733.49, stdev=22506.96, samples=944 iops : min= 6696, max=46777, avg=38840.01, stdev=2813.37, samples=944 write: IOPS=16.6k, BW=130MiB/s (136MB/s)(15.2GiB/120002msec); 0 zone resets slat (nsec): min=913, max=3425.1k, avg=5941.29, stdev=11093.02 clat (usec): min=301, max=201695, avg=2711.91, stdev=6906.19 lat (usec): min=324, max=201698, avg=2717.85, stdev=6906.22 clat percentiles (usec): | 1.00th=[ 1106], 5.00th=[ 1434], 10.00th=[ 1631], 20.00th=[ 1844], | 30.00th=[ 2040], 40.00th=[ 2180], 50.00th=[ 2343], 60.00th=[ 2474], | 70.00th=[ 2638], 80.00th=[ 2835], 90.00th=[ 3130], 95.00th=[ 3425], | 99.00th=[ 4359], 99.50th=[ 5342], 99.90th=[103285], 99.95th=[193987], | 99.99th=[200279] bw ( KiB/s): min=21968, max=163208, per=100.00%, avg=133093.00, stdev=9657.89, samples=944 iops : min= 2744, max=20400, avg=16635.00, stdev=1207.25, samples=944 lat (usec) : 100=0.01%, 250=0.01%, 500=0.13%, 750=1.04%, 1000=4.66% lat (msec) : 2=41.95%, 4=51.32%, 10=0.59%, 20=0.01%, 50=0.11% lat (msec) : 100=0.02%, 250=0.17% cpu : usr=3.95%, sys=10.33%, ctx=2211187, majf=0, minf=149 IO depths : 1=0.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=100.0%, >=64=0.0% submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.1%, 64=0.0%, >=64=0.0% issued rwts: total=4644062,1989240,0,0 short=0,0,0,0 dropped=0,0,0,0 latency : target=0, window=0, percentile=100.00%, depth=32Run status group 0 (all jobs): READ: bw=302MiB/s (317MB/s), 302MiB/s-302MiB/s (317MB/s-317MB/s), io=35.4GiB (38.0GB), run=120002-120002msec WRITE: bw=130MiB/s (136MB/s), 130MiB/s-130MiB/s (136MB/s-136MB/s), io=15.2GiB (16.3GB), run=120002-120002msecDisk stats (read/write): sdd: ios=5931652/2543396, sectors=94906432/40694712, merge=0/317, ticks=11765239/6307868, in_queue=18073398, util=96.20%
输出结果详解
读取性能
read: IOPS=38.7k, BW=302MiB/s (317MB/s)(35.4GiB/120002msec)
延迟指标（latency）
slat (nsec): min=785, max=3517.1k, avg=5204.50, stdev=9422.74clat (usec): min=55, max=201863, avg=2136.30, stdev=6055.59 lat (usec): min=153, max=201866, avg=2141.50, stdev=6055.62
| | | | |
| | | | I/O提交延时：fio将I/O请求提交给内核的时间 |
| | | | |
| | | | |
延时百分位数
clat percentiles(usec): | 1.00th=[ 685], 5.00th=[ 914], 10.00th=[ 1045], 20.00th=[ 1254], | 30.00th=[ 1450], 40.00th=[ 1696], 50.00th=[ 1893], 60.00th=[ 2057], | 70.00th=[ 2212], 80.00th=[ 2376], 90.00th=[ 2638], 95.00th=[ 2868], | 99.00th=[ 3490], 99.50th=[ 4146], 99.90th=[102237], 99.95th=[189793], | 99.99th=[200279]
解读：
P50 = 1893 μs：50%的读请求在1.89ms内完成（中位数）
P99 = 3490 μs：99%的读请求在3.49ms内完成
P99.9 = 102 ms：最差的0.1%请求需要超过100ms（尾延迟！）
P99.99 = 200 ms：极端情况下有200ms延迟
💡 重要：P99+的尾延迟非常高（100-200ms），这可能是磁盘瓶颈或GC导致的，对数据库性能影响很大。
带宽和IOPS分布
bw (KiB/s): min=53589, max=374230, avg=310733.49, stdev=22506.96, samples=944iops: min=6696, max=46777, avg=38840.01, stdev=2813.37, samples=944
采样944次，IOPS波动范围6.7k ~ 46.8k，标准差2813
写入性能
write: IOPS=16.6k, BW=130MiB/s (136MB/s)(15.2GiB/120002msec)
写入延迟
slat (nsec): min=913, max=3425.1k, avg=5941.29, stdev=11093.02 clat (usec): min=301, max=201695, avg=2711.91, stdev=6906.19 lat (usec): min=324, max=201698, avg=2717.85, stdev=6906.22
写入平均延迟2.7ms，比读取的2.1ms略高，符合预期。
写入延迟百分位数
| 99.00th=[ 4359], 99.50th=[ 5342], 99.90th=[103285], ...
延迟分布直方图
lat (usec): 100=0.01%, 250=0.01%, 500=0.13%, 750=1.04%, 1000=4.66%lat (msec): 2=41.95%, 4=51.32%, 10=0.59%, 20=0.01%, 50=0.11%lat (msec): 100=0.02%, 250=0.17%
关键发现：
CPU使用率
cpu: usr=3.95%, sys=10.33%, ctx=2211187, majf=0, minf=149
I/O深度统计
IO depths: 1=0.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=100.0%
✅100%时间保持iodepth=32，说明磁盘能跟上队列深度，没有出现队列积压不足的情况。
submit: 0=0.0%, 4=100.0%, ...complete: 0=0.0%, 4=100.0%, ...
批量提交/完成：每次批量处理4个I/O，符合libaio的批处理特性。
I/O总量统计
issued rwts: total=4644062,1989240,0,0
磁盘级别统计
sdd: ios=5931652/2543396, sectors=94906432/40694712, merge=0/317, ticks=11765239/6307868, in_queue=18073398, util=96.20%
⚠️ util=96.2%是关键指标：磁盘已经接近100%繁忙，这是P99.9延迟飙升的根本原因！
