Solaris Performance and Tools: DTrace and MDB Techniques for Solaris 10 and OpenSolaris

4.8. Disk Saturation

A sustained level of disk saturation usually means a performance problem. A disk at saturation is constantly busy, and new transactions are unable to preempt the currently active disk operation in the same way a thread can preempt the CPU. This means that new transactions suffer an unavoidable delay as they queue, waiting their turn.