If I have two switches connected to one another by a fibre link, and each of those switches is also connected into a local switch, and those two local switches are linked, I'm correct in thinking that irrespective of VLAN's or any L3 configuration, I'll have an L2 loop that STP/RSTP will need to sort out aren't I?
VLAN 100 and VLAN 200 will only exist on the top two switches so the link between those two switches will be only handle tagged traffic on VLAN 100 and VLAN 200.
The switches are dedicated to iSCSI and vMotion traffic and only need physically connect to the main network to allow management of the switches and of the iSCSI SAN.
One option would be to keep them physically separate and put a basic firewall between them and the main LAN doing away with the loop.
Thanks ever so much.
Yes, this would be a loop for which you would need STP.
When you have trunks which don't carry all VLANs everywhere, you want to use some care in selecting the switch to be STP root. In particular, if either of the bottom switches is the STP root, then the top switches will resolve the loop by blocking the trunk forming the top of the box -- which is the only transit for VLAN 100 and 200, which I suspect is undesirable.