Watch CPU and disk statistics live to locate saturated devices and long wait times. 27.03.2026 | reading time: 3 min When a server feels sluggish, check disk I/O with iostat; it reports CPU and device-level I/O statistics so you can spot saturated disks and long wait times, not just vague slowdowns. Live monitoring example Run iostat in extended mode and watch an interval to see realtime behavior: ```bash iostat -x 1 3 Linux 5.4.0-42-generic (server) 03/27/2026 _x86_64_ (4 CPU) avg-cpu: %user %nice %system %iowait %steal %idle 2.00 0.00 1.00 5.00 0.00 92.00 Device r/s w/s rkB/s wkB/s rrqm/s wrqm/s avgrq-sz avgqu-sz await r_await w_await svctm %util sda 0.10 20.00 1.00 400.00 0.00 0.20 25.00 0.50 6.00 0.10 10.00 0.30 6.00 sdb 0.00 0.50 0.00 10.00 0.00 0.00 20.00 5.20 150.00 0.00 150.00 2.50 75.00 # Here sdb shows high avgqu-sz and %util, indicating saturation on sdb ``` Keys to read the numbers Focus on a few columns: "%util" shows device busy percentage and values near 100 indicate saturation; "avgqu-sz" is the average queue length and reveals backlog; "await" is average I/O wait including service time; "svctm" is average service time but can be misleading on modern kernels, so prefer await and %util; remember the first iostat report is since boot, subsequent interval reports show activity per interval, and use flags like -x for extended, -p for partitions, -m for MB/s, -t for timestamps and -y to skip the since-boot report. When to reach for other tools iostat tells you which device is hot; use that information to drill down: run iotop to see per-process I/O, vmstat to get quick CPU/memory/I/O trends, sar for historical datasets, dstat for combined streams, or atop and collectl for long-running collection with more facets; correlate with application logs while you reproduce the load. Next steps Practice reading the columns during real workloads and combine iostat snapshots with process-level and historical tools to find the root cause; deepen skills and consider formal certs like CompTIA Linux+ or LPIC-1 and intensive exam preparation at bitsandbytes.academy to turn this knowledge into career-ready competence. Join Bits & Bytes Academy First class LINUX exam preparation. utilities storage troubleshooting
