I see that is possible to mix IOM6 with IOM12 using the correct version of Ontap that allows this and a lot of examples of adding new IOM12 shelves on existent IOM6 stacks (very common since IOM6 was discontinued)
But I don't see examples of adding old IOM6 shelves on existent IOM12 stacks.
Current: Fas2750+1 shelf DS224c
Plan: Fas2750+1 shelf DS224c+1 shelf DS2246 at the end.
ONTAP support for mixing IOM6-based and IOM12-based shelves in the same stack An enhancement has been made in ONTAP to allow intermixing of IOM6-based shelves with IOM12-based shelves in the same stack. Only one speed transition is allowed. For example, a single speed transition within a stack having two IOM6 shelves and two IOM12 shelves is depicted as: Controller <-> IOM6 <-> IOM6 <---> IOM12 <-> IOM12 <-> Controller NOTES: This enhancement requires: - IOM12 firmware 0260 and later - IOM12E firmware 0210 and later
Originally, Mixing of IOM6 and IOM12 on the same stack is not supported. You would need to replace IOM6 with IOM12 in DS2246 (that is supported) or better connect in separate stack.
Starting with ONTAP version 9.7 P4, a new functionality to support a single speed transition from 6Gb to 12Gb in a SAS storage stack. This enables storage expansion of existing 6Gb stacks with 12Gb shelves.
If you read the ONTAP 9 release notes and changes in ONTAP 9.7 (Hardware support updates).
Keep in mind, Only a single speed transition is supported in a mixed stack. You cannot have additional speed transitions. For example, you cannot have two speed transitions within a stack, which is depicted as Controller<-> IOM6 <-> IOM6 <---> IOM12 <-> IOM12 <---> IOM6 <-> Controller.
But there is a note at Hardware Universe that states the following:
Only IOM6 CIRCLE ports are allowed to connect to IOM12 ports using a transition cable. Attempts to connect IOM6 SQUARE ports to IOM12 ports result in the connection being disabled at the IOM12 as a wiring error. Cable must be fully removed from both IOMs to reset.
Well, my plan is to add a DS2246 IOM6 at the end of IOM12 stack, and according to the statement above, we can't connect Shelf-to-Shelf cable from existent shelf (IOM12) to this new shelf DS2246 using its SQUARE port (our natural choice). So my conclusion is that mixing IOM12 with IOM6 is only valid when adding a IOM12-Shelf to a existent IOM6-Stack, and no other way (IOM6 Shelf to a existent IOM12-Stack). Am I right?
You cannot have two speed transitions within a stack, which is depicted as Controller<-> IOM6 <-> IOM6 <---> IOM12 <-> IOM12 <---> IOM6 <-> Controller. To achieve a multi-path HA, you always going to have a ion12 connected back to the controller.
I think since one speed is allowed, you need to have an outage. Connect the iom6 first then add the iom12 to the stack.