Wait, just a question: is the latest one you have on the group a JG312A or what?
If so (the Switch is a JG312A) then all these models:
- HPE 5500-24G-4SFP HI Switch with 2 Interface Slots (JG311A)
- HPE 5500-48G-4SFP HI Switch with 2 Interface Slots (JG312A)
- HPE 5500-24G-PoE+-4SFP HI Switch with 2 Interface Slots (JG541A)
- HPE 5500-48G-PoE+-4SFP HI Switch with 2 Interface Slots (JG542A)
- HPE 5500-24G-SFP HI Switch with 2 Interface Slots (JG543A)
belong to the same HPE 5500 HI Switch series or Hardware platform (references on QuickSpecs here and Datasheet here) and so using/mixing them (JG312A, JG542A and JG543A) in a IRF Stack (up to nine units) should be supported provided that you, in deploying/planning that stack, will:
- follow the HPE 5500 HI Switch series IRF Configuration Guide for requirements/restrictions/best practices (just as example read this): the guide can be found here <-- it's not exactly up-to-date with regard to the actual Release 55xx software release but it should be good enough to start with (also consider to read the HPE 5500 HI Switch series Installation Guide here).
- ensure that all units partecipating to the IRF Stack use the same exact updated Comware 5.20 software version (actually, as of today, it is Comware 5.20 Release 5501 P27, see here).
Usage of SFP+ ports (present on front panel/provided by expansion slots' modules) or 10GE ports (provided by expansion slots' modules) is not only supported but a requirement (see binding restrictions/IRF configuration guidelines on the IRF Configuration Guide on what "Physical SFP+ Port <--> Logical IRF Port" binding combinations are really supported by those type of Switches especially when you start considering [*] IRF Link Aggregation with IRF Ring Topology or with IRF Daisy Chain Topology).
[*] I mean...when you consider to deploy IRF Link Aggregation instead of using just a single physical port for each Logical IRF Port (up to three physical SFP+/10GE ports can be aggregated together to form each Logical IRF Port on each involved Switch) concurrently with IRF Ring Topology (IRF Port 1 and 2 on each Switch, IRF Port 1 of Switch 1 to IRF Port 2 of Switch 2, IRF Port 1 of Switch 2 to IRF Port 2 of Switch 3, IRF Port 1 of Switch 3 to IRF Port 2 of Switch 4...and so on...until you close the loop into IRF Port 2 of the Switch 1) or concurrently with IRF Daisy Chain Topology (as above without closing the loop).
Edit: eventually, HPE Knowledge Articles like this one explain when IRF Stack can't be formed due different HPE Switch series: HPE 5500 HI versus HPE 5510 HI.