Key Performance monitor counters to identify performance problems

PhysicalDisk

1. PhysicalDisk: Avg. Read Queue Length Should be less than 2
2. PhysicalDisk: Avg. Write Queue Length Should be less than 2
3. PhysicalDisk: % Disk Time more than 50% indicates a bottleneck

Reference: http://www.computerperformance.co.uk/HealthCheck/Disk_Health.htm