My environment consists of two FAS3140's in an Active/Active cluster and two DS4243 disk shelves. There are two quad port HBA's in each controller. As you can see from my diagram below, each HBA has two unused SAS ports. I'm adding a third DS4243 disk shelf and not sure if i should create a third stack or if this is even an option. Or is it best to add it to an existing stack? Any help is appreciated. Thank you.
You could create a 3rd stack and that is supported. If the same disk type (SAS or SATA), I would add the third shelf to one of the existing stacks though. It is also supported to switch disk types within the stack but we still prefer keeping them separate. You aren't going to hit a bandwidth limit with 24GB/sec (3GB*4 lanes=12GB *2 paths) to each stack and it will be less cabling and easier to add to an existing stack.