As it illustrate below this is FAS 8020 attached to 3 disk shelves DS2246 connected by sas cable .
i need to add new disk shelf DS4246
I do not know what the correct way to add the new disk shelf. Do I add it in a new stack or add it with the rest of the disk shelves in the same loop? What is the difference between the two methods in terms of benefit ?
Whatever the correct way, can anyone help me by clarifying in the drawing how the cables will be connected when adding the new disk shelf?
1- what is differance between connecting disk shelf in new stack and connecting in same stack (loop)?
A new stack will use a different set of SAS ports on the controllers. Smaller level models can only have 1 stack. Like the A2xx series and the FAS2xxxx series as they only have 2 SAS ports per controllers. Other platforms can have more than 1, depends on the onboard ports and what expansion cards they have. the 8020 for example, but default can only have 1 stack using the onboard ports, but you can add is SAS cards to add additional stacks.
There are rules about how many shelves you can have in a stack. https://hwu.netapp.com has the info of what is supported/best practices when it comes to per controller, per shelf type. For example for AFF, the recommended is 2 shelves per stack and the max is 4 shelves per stack. So if you put 8 SSD shelves in a stack, it might overwhelm the bandwidth between the disks and the controllers. For 6Gb IOMs you can add.. 10? shelves in a stack, but if you start to add SSD shelves, the number of SAS shelves goes down. The number of shelves in the stack can affect the throughput on the backplane. Too much IO to the disks and you can cause a bottle next.
It's also helpful if you have the option, to have a SAS stack and a SATA stack. Some platforms you don't have a choice, but if you have an 8200 or 8040 model. you could separate them out that way.
2- Can you illustrate how to connect disk shelf in new stack?
There's diagrams in the above linked cabling doc. I can't find a drawing of a FAS8020 specifically. But if you look at the install guide for the 8040 and 8060 you can see the controllers with two shelves using the onboard ports.