If I understand the "zone per initiator" model, each zone will contain:
- One and only one initiator HBA
- One or more target HBAs
Is this correct?
First of all, I would like to be clear on something. While I have worked with FC SAN for several years, I do not consider myself an expert. I based my decisions to deploy zones with one initiator and one zone on two things.
First, I read best practices documents and manuals from my SAN switch manufacturer. I do not have the document handy, so I cannot reference it directly. From what I recall, the Cisco best practices guide for NX-OS (I cannot recall whether it was 3.x or 4.x) indicated that for small SAN fabrics, placing more than two (2) HBAs in a zone would not create issues; however in large SAN environments, the wasted resources could become an issue.
Second, I worked in an environment where the SAN switches were daisy-chained together instead of kept in a strict A-B topology. This was done due to a combination of physical plant constraints, a requirement to manage all zones and zonesets from one SAN switch, and a lack of understanding of why strict A-B topologies are such a very good idea. In this environment, each zone contained all initiator HBAs on the host, all target HBAs on all required SAN controllers, and all target HBAs on all tape drives. This model made some aspects of administration easier. Unfortunately, it added a very difficult problem. Because there was more than one SAN switch but only one SAN fabric and because all initiator HBAs on a host could see all target HBAs on the necessary storage controllers, it was very easy for a host to chose an initiator-to-target path that crossed the inter-switch links. The SAN switches were capable of line speed between ports on the same switch. But the inter-switch links contained only two (2) interfaces per switch. In other words, the inter-switch links could easily become a bottleneck to SAN traffic. To make matters worse, the hosts could not easily identify which initiator-to-target connections crossed inter-switch links and which remained within a single switch. As a result, I strongly recommend using a strictly A-B SAN topology.
That being said, if my customers have maintained a strict A-B topology and the number of wasted connections is insignificant to the switch's/fabric's maximum number of connections, then I wouldn't worry about putting more than two (2) HBAs per zone.
On the bright side, since HBAs can be members of more than one zone, it may be possible to replace the more-than-two-HBA zones with several only-two-HBA zones without client disruption. However, I would confirm that with my SAN switch manufacturer (and some testing if possible) that such a migration is supported.
