Install AIX on external disk(from Clariion CX4-120)

Hope this helps:

from a ibmsystems wweb article:
http://www.ibmsystemsmag.com/aix/december06/focusonstorage/6270p4.aspx

Following are the steps Lockheed Martin use to test boot from SAN (Note: These procedures are based on using a QLogic-branded HBA. Emulex HBAs will differ slightly in the procedure.):

1.Select the first Host Adapter listed in the BIOS
2.Select "Configuration Settings."
3.Select "Host Adapter Settings."
4.Ensure that "Host Adapter BIOS" is "Enabled"
5.Press "Esc" and return to "Configuration Settings."
6.From the Configuration Settings menu, select "Selectable Boot Settings."
7.Select "(Primary) Boot Port Name, Lun:".
8.On the "Select Fibre Channel Device" screen, select the first device shown (there should be only one).
9.If another screen comes up, select "Lun 0 Supported".
10.Press "Esc" twice to exit the Selectable Boot Settings and the Configuration Settings menus.
11.Select "Save Changes" and press "Enter."
12.Save and exit Fast!UTIL.
13.Reboot the server.

you can also reference AIX Connectivity guide, there is a section for booting from SAN.

https://powerlink.emc.com/nsepn/webapps/btg548664833igtcuup4826/km/live1/en_US/Offering_Technical/Technical_Documentation/300-000-608.pdf

it is good info for xSeries and Windows, but not for pSeries and AIX.
Thanks anyway