As Peter said, the only real option here is to use aggregate mirroring between the two controllers. So here is what it would look like:
Filer01:aggr1 (read/write) is mirrored to Filer02:aggr1 (read only)
I'm not sure if this is quite what you were referring to but with 7-Mode (as opposed to Cluster or C-Mode) this is really the only option to achieve what I think you are describing.
But that brings me to a big question: Why?
If this is 7-Mode and is configured as an HA pair then you have fault tollerance in the event of a controller failure as the other controller will take over but that requires that each loop be present on each controller.
Each 3020 controller has four onboard FC ports, I'm assuming the following configuration (assuming DS-14 disk shelves with AT-FCX modules and that you don't have an FC PCI cards installed)
Filer01, port 0a - initiator - connected to loop1 (SATA)
Filer01, port 0b - initiator - connected to loop2 (SAS)
Filer01, port 0c - not used or set as a target for client connections
Filer01, port 0d - not used or set as a target for client connections
Filer02, port 0a - initiator - connected to loop1 (SATA)
Filer02, port 0b - initiator - connected to loop2 (SAS)
Filer02, port 0c - not used or set as a target for client connections
Filer02, port 0d - not used or set as a target for client connections
If this is the case, then you are in HA but don't have dual paths to each loop which is not recommended but will work.
Is this accurate?