Joining stacks of shelves is indeed possible provided you don't exceed the stack limits. If the shelves are DS2246 or DS4246 you'll be fine, but the HDD limit per stack is 240 devices so if the shelf type is DS4486, you can only have 5 per stack. Also, remember that your FAS8200 has miniSAS-HD ports and the IOM6 shelves have QSFP ports, so you're going to need different cables to do the procedure below. Now, assuming you're good on shelf types and cables, on to the procedure:
Abbreviations used below:
Controller A or B -> CA, CB
IOM-A or IOM-B -> IA, IB
Shelf # -> S##
You should currently have the following existing connections:
CA:0a -> S01:IA:Square
S01:IA:Circle -> S02:IA:Square
...
S04:IA:Circle -> CB:0d (remove this)
CA:0c -> S11:IA:Square (remove this)
S11:IA:Circle -> S12:IA:Square
...
S14:iA:Circle -> CB:0b
Make New Connection: S04:IA:Circle -> S11:IA:Square (Requires QSFP/QSFP cable)
Before continuing, wait a bit for SAS paths to settle.
Existing connections:
CB:0a -> S01:IB:Square
S01:IB:Circle -> S02:IB:Square
...
S14:IB:Circle -> CA:0d (remove this)
CB:0c -> S11:IB:Square (remove this)
S11:IB:Circle -> S12:IB:Square
...
S14:IB:Circle -> CA:0b
Make New Connection: S14:IB:Circle ->S11:IB:Square (Requires QSFP/QSFP cable)
Before continuing, wait a bit for SAS paths to settle.
Now the following ports should be free:
CA:0c, CB:0d, CA:0d, CB:0c
On both controllers, move the connection currently in 0b to 0d to maintain best practices.
Now the following ports should be free:
CA:0b, CB:0b, CA:0c, CB:0c
Use these for your new shelf.
