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High Avg. Disk Queue Length

The fact that the line stays at the top of the graph does not necessarily indicate there is a problem.  The default Avg. Disk Queue Length graph scale is 100 so any value >= 1 will peg the graph.
As a general rule, Avg. Disk Queue Length should not consistently exceed 2 times the number of physical disks in the array.  A higher number indicates a disk bottleneck.  This can be:
1)  due to excessive paging (are other apps besides SQL Server running on the box)
2)  an indicator that database tuning is needed (e.g. adding indexes)
3)  cause by inadequate number of disks to satisfy workload

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