Performance of stacked switch

[Cooky]

I'm installing a stack of 3x 3750G switches, which are inter-connected w/ StackWise cables.
Are stacked switches truely act as one switch w/o any performance penalty if a packet has to traverse from one switch to another in the same stack?

Would it be better to arrange the ports together on the same switch if I know they'll mostly generate local traffice among themselves?

Another question I have is sould I try to distribute ports among the stacked switches as much as possible or is the stack really functioning as a unified stack??
For instance, I've got 3x 24-port 3750G's; thus a total of 72 ports. If I currently have only 24 objects (clients or switches), should I plug 8 in each switch or it doesn't make a difference if I plug all 24 objects into the same switch?

 

[spidey07]

It acts like one big chassis based switch - like a 4500 or 6500.

the stackwise cables act like a backplane. Doesn't matter where you plug stuff in at.

in the future try to use 48 port switches instead of 24.

Also make sure you force the master. Don't let it pick one.

 

[jlazzaro]

just to add on what spidey said, just make the switch priority of one of the 3750's higher than the others and it should be elected as the master.

also, its good to renumber the stack as well. when you first hook them up, they dont automatically number themselves in order. its confusing if your making changes to a gig port on the top switch and while you would think that port would be gig 1/0/1, it could be gig 3/0/1 or gig 2/0/1. just go through show switch command and re-number them the way they are racked to make your life a little easier...

 

[Cooky]

yup, I know all about the master election and switch renumber...was just curious about the technology.
So pretty much the answers to my questions are: yes, no, no?

 

[jlazzaro]

correct.

 

[Pheran]

Originally posted by: Cooky
I'm installing a stack of 3x 3750G switches, which are inter-connected w/ StackWise cables.
Are stacked switches truely act as one switch w/o any performance penalty if a packet has to traverse from one switch to another in the same stack?

Cooky,

The 3750 uses a 32 Gbps shared ring architecture - all the frames use the ring backplane, even the ones that are forwarded between two ports on the same switch. So, there are no worries about how to distribute your ports among the stack. On the downside, your stack is oversubscribed since you have 72 Gbps worth of ports, but that should not be a problem unless you're going to put an extremely heavy load on this stack.

 

[Pheran]

Originally posted by: spidey07
in the future try to use 48 port switches instead of 24.

Usually I would agree with this, but the 3750 pricing structure is such that you save money if you don't need the port density, so the 24 port switches may make sense depending on your situation. Plus, you're going to heavily oversubscribe the StackWise ring pretty damn fast if you start stacking 3750G-48 switches, considering that it's already oversubscribed with a single switch. This may or may not matter depending on your application.