Are the disks fast enough?

Physical Disk (instance)\Disk Transfers/sec

To monitor disk activity, we can use this counter. When the measurement goes above 25 disk I/Os per second then you’ve got poor response time for your disk (which may well translate to a potential bottleneck. To further uncover the root cause we use the next mentioned counter.

Physical Disk(instance)\% Idle Time

This counter 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. Why not use Physical Disk(instance)\% Disk Time instead? Well, we will cover this in details in future post.

(Source: Mitch Tulloch, Windows Networking)

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