I'm repurposing an old SAN device for some additional non-critical storage on a VM on a 3-host S2D cluster. I can't dedicate the switches at the moment like what seems to be recommended so I need some advice in setting up the VLAN correctly so the VM can communicate with the SAN target. I've included a network diagram below.
The SAN target is connected to two switches with a SAN VLAN (50) set up, ports are untagged and jumbo frames enabled.
I think I need to put in another link between the core and the SAN switch but I'm not sure how to tag the ports on either end to achieve the connection.
I'm not sure where your storage is consumed as the hosts on the bottom have no VLAN 50 - you're not routing in between, are you? You'll always want a storage path that's as short and simple as possible.
When you use two switches (redundant data paths) you should always use two VLANs. Two VLANs provide more reliable separation between data paths - mixing them might cause non-obvious failure modes with no (clean) failover.
Accordingly, you should also use two independent links (not blocked by STP and not in LAG) to your core switches and two redundant link on each host (may be combined with other iSCSI VLANs, as required).
You shouldn't tag towards the storage appliance and the hosts (with dedicated NICs) for simplicity, but sometimes there are good reasons to do so. You should definitely tag between SAN and core switches.
Jumbos are often not worth the trouble with modern offloading NICs.