Disk transfer time measures the time it takes in milliseconds to transfer data between disk and memory. The metric includes disk reads and disk writes.
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If disk transfers are taking consistently longer than 50 milliseconds a disk bottleneck may be developing. The Disks - Transfer Time alarm is raised when the transfer time exceeds 50 milliseconds.

When this alarm is raised, refer to the Windows Server | Disks Drilldown | Physical Disk Activity page | Transfer Time chart.