Disk operations.
WHAT IT MEASURES
How much reading and writing to disk your account does.
WHAT CONSUMES IT
Database queries Log writing Cache files being written Backups Large file transfers Email delivery
THE SYMPTOM
Slowness that does not correspond to processor or memory use.
WHAT USUALLY CAUSES IT
A backup running A large import or export Excessive logging A plugin writing constantly Database queries reading large amounts
WHAT TO DO
Move backups to quiet periods Reduce logging Enable caching, which reduces database reads Find anything writing excessively
THE LOGGING POINT
Debug logging left enabled writes continuously and grows a file indefinitely.
Common after someone diagnosed a problem and forgot to turn it off.
WHAT TO CHECK
Whether any log file is growing rapidly.
