I was whiteboarding a switch migration today with one of the DCR people, and it occurred to me:
If you can visualize the data’s path through the system, your life gets a lot easier.Â
If you can see the path the data is going to take through the San, I.E. from Switch1, Blade1, Port4 through an ISL to Switch2, to Switch 2, blade 2, port 16.Â you put yourself in a better position to shorten that path.
First, cut the ISL’s.Â Unless you can absolutly avoid it, don’t pass data down an ISL link.Â Pushing data through an ISL does two things.Â It creates a bottleneck where there may not be enough bandwidth to handle multiple hosts.
Second, keep the intra-switch hops to a minimum.Â If you can do it, plug the storage and the higest performing hosts into the same grouping of ports.Â Most switches use 4 port ASIC’s, and if you look at the switch you’ll see that the ports are grouped by ASIC.
However, the 32port Cisco blade is an exception, uses basically the same ASIC, but shares the bandwidth over 8 ports, so keeping that in mind it’s best to connect the lower performing hosts (Windows?) to those ports, and definately *DO NOT* connect ISL’s to the 32 port blades.