Performance Counters - Disks Fast Enough?

Let's look at a couple of indicators of well-functioning hard disks in your system. Watch the Physical Disk (instance)\Disk Transfers/sec counter for each physical disk and if it goes above 25 disk I/Os per second then you've got poor response time for your disk. A bottleneck from a disk can significantly impact response time for applications running on your system, so you should investigate this further by tracking Physical Disk(instance)\% Idle Time, which measures the percent time that your hard disk is idle during the measurement interval, and if you see this counter fall below 20% then you've likely got read/write requests queuing up for your disk which is unable to service these requests in a timely fashion. In this case it's time to upgrade your hardware to use faster disks or scale out your application to better handle the load.