ONTAP Hardware

SAS Cabling - splitting a SAS Stack Without Shutdown


I have the following situation

FAS6290, CDOT 8.2.3

It has 2 mixed (SSD & SAS) stacks

- Stack #1: 4xDS2246x600GB SAS + 1xDS2246x200GB SSD (2 x sas cables to controller 1, 2 x sas cables to controller 2)

- Stack #2: 4xDS2246x600GB SAS + 1xDS2246x200GB SSD (2 x sas cables to controller 1, 2 x sas cables to controller 2)

SSD shelves are the first (last) of the stack in both stacks above.


I want to separate SSD and SAS shelves, splitting each of the stacks in 2, WITHOUT SHUTDOWN. That will end with 4 stacks (2 x SAS, 2 x SSD)


If I remove ONLINE the SAS cables between the SSD shelf and the first of the SAS shelves in each stack, will those 2 stacks be automatically converted in 4 stacks?

Can I then close these 4 stacks with 8 SAS cables going back to the controllers to restore the redundant connection?


It is clear I can do this WITH a shutdown, but can it be done WITHOUT?



Online removal is supported only for completely unused shelves. What you are doing is effectively removing shelves from stack. Go figure ...


Thanks for your answer. I had already read this:


Hot-removing disk shelves in systems running Data ONTAP 8.2.1 or later



but I don't think it fits what I am doing, since I am not removing the shelf (all shelves remain connected to both controllers at any time)


May be the following quick hand-drawing makes it more clear.

In step #1, I remove 2 SAS cables, but the removal keeps all shelves connected (single path, instead of dual).

In step #2, I reconnect the 4 disconnected shelf SAS ports, but to new SAS ports in the controller.


It's clear I can power down the storage and do this changes offline, but can I do them without disrupting service?




Well, hot cable move between adapters is supported as of 8.2.1; see kb2023388. The catch is "between adapters". Not between shelf and adapter 🙂 I think this is one of those twilight zones where you do not get direct answers.


That looks dicey.  But I suspect odds of success would improve if you did a takeover/giveback between step 1 and step 2 so each node gets to boot in a dual stack single path ha config.  Interesting lab experiment, but wouldn't try it on a production filer.  If you do try it, tell us if it panics on you.