The Disk Reads Per Second alert provides the rate of read operations on the disk. A high number of disk reads may indicate that SQL server is executing poorly performing queries. Note that this alert is disk specific.
This alert is raised based on the diagnostic data collection interval specified in Server Properties. Note that you need to enable this alert first in the Alert Configuration window to rise.
The Disk throughput chart provides a graphical analysis of the number of disk reads and writes over time.