10-05-2010 05:36 AM
Attached is a simplified presentation of our present SAN...
Soon, we will add another ISL to this fabric. This will be a connection between FC-switch1 and FC-switch4. This ISL will be configured at speed 2G.
Routing on all switches is configured as default, as shown below.
Current Policy: 3 0(ap)
3 0(ap): Default Policy
1: Port Based Routing Policy
3: Exchange Based Routing Policy
0: AP Shared Link Policy
1: AP Dedicated Link Policy
What will happen to traffic between the storage systems on FC-switch2 and FC-switch4? Will it be load-balanced between the two paths or will it use the quicker path over FC-switch3?
If you need more information, I would like to hear... We have great discussions about it, but we can't come to a conclusion.
I hope we will with your help.
10-22-2010 01:46 AM
This is all based on FSPF and link costs.
It also depends on how many ISL's you have between 1 and 4 (which will bring the linkcost down). By default it will use the link with the lowest cost if you have only 1 ISL so yes it will traverse switch 3 and not 1. If you set the costs equal (linkcost command) than it will use an round robin algorithm per session. Once that session is esablished it will stay there. (Unless there is a logout and subsequent login.)
I don't know the rest of the setup but a link between 2 and 4 would be very handy. I guess you can figure out which path its going to use then.
10-23-2010 03:25 AM
Well, I prefer the traffic to travers switch 3, because of the 4 GB ISL. Buth the cost for the 2 GB ISL is the same as for the 4 GB ISL...
Based on link cost, path selection cannot be performed.
Round Robin path selection sounds nice, but because of the different speeds of the ISLs isn't preferrable I think.
Or can I just connect switch1 and switch4 without worrying about path selection?
10-25-2010 10:22 PM
If you really want to direct certain traffic over a particular ISL you can use so called TI zones. (Traffic Isolation zones). Look in the manual how to set that up. You might want to do some reading an planning beforehand.