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Measuring SAN performance

Hi Marc,

How do I measure the SAN performance? How do I know whether the network I have configured is efficient enough?

Thanks for your valuable time.


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I/O measurements have typically been made by host software. It's not easy to use and difficult to interpret. There are specific products for the different platforms because they have to work at the kernel level. Very tough stuff to write and the market size for it is small. You will probably need an experienced SE to help you with it.

There are basically two things to measure in a SAN: latency and channel utilization. Neither are easy to measure and you will probably need to calculate the results. Latency is the harder of the two and you probably don't have a way of measuring it, much less finding out where latency problems might be. Latency is added in the HBA, the switch/hub and in the subsystem controller. Latency is also inserted by any virtualization processes. I think Finisar, Ancot or some of the other FC analyzer companies would have products that simulate network traffic, but I don't know that they measure latency.

The other measurement is bandwidth utilization. This can be done by transferring a known quantity of data of the network and dividing by the time and calculating against the total bandwidth. There are probably more precise utilities for doing network simulation (again through the FC analyzer companies) but I haven't used them.

The important thing to know is that SAN equipment tends to be over-engineered when compared to of Ethernet/IP equipment. That means it is much more likely to sustain high performance over heavy workloads than comparable Gigabit Ethernet switches. That could change in the future when specialized Gigabit Ethernet storage switches come to market.

Design your SAN conservatively and try to connect entities together through ports that share the same ASIC - this will save your bandwidth on switch backplanes.

Regards,
Marc Farley


This was first published in August 2001

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