Performance Monitor counters to analyze disk bottleneck

Counter Description Expected Value
% Disk Time Percentage of time disk was busy with read/write activities. Average value < 85%
Current Disk Queue Length Number of outstanding disk requests at the time performance data is collected Average value < 2 per disk
Avg. Disk Queue Length Average number of queued disk requests during the sample interval Average value < 2 per disk
Disk Transfers/sec Rate of read/write operations on disk Maximum value < 400 per disk
Disk Bytes/sec The rate at which bytes are transferred to or from the disk during read or write operations.
If the amount of data transfer exceeds the capacity of the disk subsystem, then a backlog starts developing on the disk subsystem, as reflected by the Disk Queue Length counter.
Maximum value < 800MB per second
Avg. Disk Sec/Read Average time in ms to read from disk Average value < 10 ms
Avg. Disk Sec/Write Average time in ms to write to disk Average value < 10 ms

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