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Linux

Load average is high but CPU usage is low

The Issue

Server feels slow. `uptime` shows load average 25. But `top` shows CPU at only 15% usage.

Root Cause

Load average counts both CPU-bound and I/O-waiting processes. High load + low CPU = I/O bottleneck. Processes are queuing, waiting for disk or network reads to complete.

How to Fix
  1. Confirm it is I/O: check `wa` (iowait) column in `top` — if high, disks are the bottleneck
  2. Find what is hammering disk: `iotop -o` (shows only active I/O processes)
  3. Check disk health: `iostat -xz 1` — look at `%util` and `await` columns
  4. Check for a runaway database query or log-write loop
  5. If NFS mounted: check if NFS server is slow or unreachable
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