Quickly spot which disks are busy and measure request rates and latencies. 16.11.2025 | reading time: 3 min When a server feels slow, the disk often hides the truth; iostat lets the administrator watch block device throughput, request rates and latency so he can decide if the storage is the problem. Live example: capture extended stats Run iostat with extended metrics and a short interval to get current device behavior: ```iostat -x -m 1 2 Linux 5.15.0-0 (host) 11/16/2025 _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 rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util sda 0.00 10.00 5.00 20.00 0.50 4.00 48.00 0.20 5.00 2.00 5.00 sdb 0.00 0.00 0.50 0.10 0.02 0.00 40.00 0.01 2.00 1.50 0.08 Device rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util sda 0.00 8.00 6.00 18.00 0.60 3.60 44.00 0.30 6.50 2.50 6.00 sdb 0.00 0.00 0.40 0.20 0.01 0.01 36.00 0.01 1.80 1.40 0.07 ``` Make sense of the columns Look for high %util to detect device saturation, watch await for end-to-end latency, and use r/s and w/s to see request rates; avgrq-sz shows average request size and avgqu-sz reveals queue depth, while svctm may be unreliable on modern kernels so treat it cautiously. Useful options to shape output Use -x for extended stats, -d to focus on devices, -p to include partitions, -m to show megabytes, -t to add timestamps and run with an interval like "1 5" to sample continuously; remember the first iostat report is an average since boot so request periodic samples to see real-time activity. When to combine other tools If iostat points to high latency or queueing, run iotop to find processes with heavy I/O, use blktrace for low-level event tracing or vmstat to correlate CPU and swap activity and build a fuller performance picture. Next steps Practice by capturing runs during peak load, compare device-level iostat output before and after tuning, and script periodic collection into CSV for trend analysis; then go deeper with tracing if needed and keep learning toward formal Linux certification to validate the skills. Join Bits & Bytes Academy First class LINUX exam preparation. storage utilities troubleshooting
