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 ResponseTime parameter of the SEN_EMC_VOLUME_CLAR and SEN_EMC_VOLUME_SYMM application classes 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 to the response time of the other LUNs to see whether one server is really getting worse I/O performance than another.

Graph – Diagnosing Slow LUNs

If the response time is low, you will need to check the amount of data that is written and read on 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.