CPU high because disk is slow
This is one of the most misunderstood performance patterns. CPU looks busy, but disk is the real bottleneck.
Common symptoms
- CPU and latency rise together
- Disk-heavy workloads slow down first
- iowait climbs with the CPU chart
Likely causes
- Slow or saturated disk
- Large sequential scans
- Too many concurrent file operations
Evidence to look for
Disk utilization near 100%
High iowait
Long disk await times
What it usually means
Threads block on IO and pile up, making CPU charts spike even though the actual compute demand is low.
What to do next
- 1Move to SSD or faster storage
- 2Reduce concurrent disk-heavy work
- 3Add caching to reduce disk reads
See what's causing your CPU
cpum.ai turns CPU, process, disk, and memory signals into plain-English explanations with evidence.
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