OK, now I know why this isn’t working. Basically any array (Nexsan speak for Raid Group) is owned by only one controller at once – and its LUNs are only delivered via a single controller.
If we’d used QLE2462s and dual-attached the X4100 then we’d see multiple paths to LUN20, but they’d all go via SB c0. If the array is failed over to SB c1 then they’d show up there instead.
What I now need to do is to set up MPxIO, configure the first paths to the LUN, then try administratively failing its owning array over to the other controller. It remains to be seen whether this will “just work” or whether I need to further configure MPxIO to know that both results are basically one and the same thing (or even if that’s actually possible).
In any regard, this is looking very good.
At the other end of the problem, we installed the trusted extensions to Solaris which appear to permit multiple NFS views. We’ll confirm or deny this shortly. TSOL is a bit of a pain to configure – hopefully we can keep the setup requirement to a minimum – if Solaris 10 grows zonable NFS service (or I build a userland NFS server which I can configure myself) this might become more straightforward.