Yeah you have pretty much worked it out.

For FCP Partner cfmode, the filer uses a feature called "FCP Proxy" to forward requests to the partner LUN.

As you said, in normal mode, primary paths are through the A port on Filer 1 and B'' port (second adapter) of Filer2.

The FCP Proxy allows MPIO s/w to maintain active-passive connection by using the VTIC adapter between the two filers to proxy commands.

As far as I know, your host requires MPIO software to achieve this. I don't think this has changed for 7G, but I haven't reviewed it yet.

Thie whole thing is possible because the B ports WWPN/WWNN are based on the Partner nodes WWNN. Thus for AIX/HP-UX types, the requirement that static S_ID and D_ID are maintained because the WWPN/WWNN don't change during failover. This keeps the MPIO software happy.

No changes on the switch are made. Both access the Filer1 LUNs via the A port on Filer1 and B port on Filer2 (FCP Proxy does the forwarding) B port WWNN/WWPN based on partner WWPN.

Hope that explains it.

Now, if you start doing mixed cfmode using the public loop/multi-ID, it will take me a little longer to explain.

--Aaron

-----Original Message----- From: Steve Losen [mailto:scl@sasha.acc.virginia.edu] Sent: Wednesday, 27 April 2005 8:23 AM To: toasters@mathworks.com Subject: How does FCP cfmode partner work?

We recently set up a new FAS960c pair of filers running 7.0.0.1 and I am trying to understand how cfmode partner works.

According to the "Block Access Management Guide for FCP" the A port on each FC adapter is for accessing local LUNs while the B port is for accessing partner LUNs. In "cfmode partner" both ports are active.

So does that mean that in normal operation (no failover) that initiators (hosts) can access a LUN on filer 1 from a B port on filer 2? That is what the manual seems to indicate.

How is this accomplished? Does it happen within the switch? Do FCP requests for a B port get forwarded to an A port on the partner during normal operation?

Obviously during a failover the surviving head takes over the disks of its partner and then satisfies requests to the B port itself.

Steve Losen scl@virginia.edu phone: 434-924-0640

University of Virginia ITC Unix Support

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