I think we may be talking about 2 different best practices that confusingly sound the same.
I suspect that you are referring to Single Initiator/Single target zoning. This is to avoid unintended communications between zone members, and limits one path per zone. If you add a 3rd member to the zone, then the zone allows all 3 members to talk to each other which is generally un-intended. Most commonly I see 1 host HBA and 2 storage ports in the same zone, and generally this works fine, however it will permit the 2 storage ports to talk to each other if one should try to log into the other (Clariion SANcopy comes to mind).
The concept I was recommending with 1:2 fan out is that one HBA port should have paths to 2 front end ports. If you follow the best practice you mentioned, that would mean you would need twice the number of zones, and not just add one more storage front end port to the existing zone.
The reason I do this is to distribute host loads over multiple ports to avoid storage front end port saturation. If your hosts are running at 8gb, and your storage is running at 8gb... then a 1:1 fan out ratio has the potential for 1 host to saturate a storage port or two. By splitting each HBA's traffic down two paths, the worst a single host can do is push the storage front end ports at 50%... I have 157 hosts connected across 32 front end ports (two T800s with 4 nodes ea), which were arranged into 8 "sets" of 4 front end ports that I manually assign hosts to when they are initially connected to the SAN.
_________________ Richard Siemers The views and opinions expressed are my own and do not necessarily reflect those of my employer.
|