Diagnosing Slow LUNs

If a system administrator complains that his servers are experiencing slow I/Os performance and that it is caused by the SAN, you may want to verify the actual response time of the LUNs the server is relying on.

The ReadResponseTime and the WriteResponseTime parameters of the SEN_I68_VOLUME class represents the average time it took to complete the read and write operations on the LUN during the collection interval. Typically, the average response time is below 10 milliseconds. You may also want to compare this value with the response time of the other LUNs to see whether one server is really getting worse I/O performance than another.

1.In the console, double-click the ReadResponseTime parameter of the storage unit you are interested in. A graph is automatically displayed in the graph pane.

2.Drag the WriteResponseTime parameter of the same storage unit in the graph.

TREE_Read_WriteResponseTime_Volume

Selecting Graph's Parameters

If the response time is low, you will need to check the amount of data that is written on and read off this LUN. The bad performance may simply be due to an abnormally large amount of data to process. Otherwise, the problem may lie between the disk array and the server, in the fiber links.