Mulitple ISLs without ISL Trunking

[Denver Osborn]

I'm working with a pretty small san and we're planning an upgrade. Due to distances between san switches we can expect 1Gb/sec performance per ISL.

If I use two brocade 4100's and multiple ISL's between the switches, will the load be balanced without ISL Trunking?

What exactly is DLS and does this work without Trunking?

Sorry if this is a stupid question, but I'm learning as it's new to me. :)

Thanks,
-denver

[Richard Tengdin · Accepted solution]

Yes, there will be static load balancing for the hosts. The fabric will use FSPF (Fabric Shortest Path First) routing to assign hosts to one ISL or the other, and they will use the assigned path exclusively until it fails, then the fabric will reconfigure and reassign ISL paths to the hosts.

Are you using 50micron core cable for your ISLs, or are the switches really more than 150m apart?

[Denver Osborn]

The distance is about 400m and using 50 micron MMF.

So without trunking it's very possible I could end up with an idle ISL?

-denver

[Richard Tengdin]

Hosts will be statically assigned an ISL when they log in to a fabric, and the assignment is done Round Robin (AFAIK).

If *all* the hosts assigned to an ISL are idle then the ISL will be idle, but it won't be a hot spare, it just won't have any workload at that moment....

[Amar_Joshi]

If the DLS is enabled you should be getting packet based load balancing. Check it with "dlsshow".

With Trunking license, you should be able to get the frame based trunking, which will fully balance the ISLs.

[Jim Paulsen]

unless you use the trunking, the load won't be balanced. While data will be passing over all paths and provide redundancy, one path will be the dominate path. Personal Experience. 4100s connected to 12000 directors with multiple ISLs... on a side note, my ISLs were on different ASICs. I don't know if that will make a difference or not. Trunking needs to be on the same ASIC, that's why I bring it up.

[SAKET_5]

just a correction in last post - trunking occurs only for ports coming from the same quad!