Ok, that was too cutsey for such a classy establishment.
When you’re building a SAN, everything should play together, in the same SAN box if you will (with my apologies to QLogic.)
When you start putting in multiple stand-alone SAN islands you increase your maintenance overhead exponentially. You also prevent the very thing that make a SAN a huge advantage over DAS.
Everything can see everything.
If you have a host and need to throw a certain type of storage at it, you can do that easily. (and if it’s already cabled you can do it from your living-room)
However, if SAN A/B are connected to one group of hosts/storage, and SAN C/D are connected to a second group of storage, and SAN E (no redundancy) is connected to even a third, you run into a problem.
*NOW* if I want Host_A (Connected to SAN A/B) to see Storage_C (Connected to SAN C/D) I have to do much more than a simple zoning change.
In the end, this is where a few well placed ISL connections can come in handy. VSAN them off so they don’t cause the fabrics to merge, create an IVR zone to route across them, and then presto. Host_A can see Storage_C with a minimum of fuss.
Or maybe a *REAL* core-edge topology even. Where you put a core switch with 24-port (fully subscribed) blades ISL’d to an edge switch, which maybe has the 4/4/40 configuration (4 8-Gig ports, 4 dedicated 4Gig ports, and 40 shared 4Gig ports)
And put one person in charge of it. Preferably someone with a touch of OCD. 😉