A while back, we purchased another Cisco UCS chassis populated with B200-M3 blades. These blades didn't come with internal hard disks, so we had to configure boot from SAN. As these were new servers, all we had to do was make the necessary changes to the Service Profile Template and then deploy it onto the blades. If the service profiles are already deployed, you will need to apply the change to the service profile for each server or the service profile template if it is an updating template.
The first thing you will need to do is select the service profile or service profile template and "modify the boot policy" under the "boot order" tab.
Next, create a boot policy. Add CD-ROM device first so that you can install the OS/hypervisor (ESXi 5 in my case). Under vHBA, select "Add SAN Boot" and then type in the name of the vHBA that will be the primary initiator.
Note: In my environment, vHBA FC_0 and vHBA FC_1 are the primary and secondary SAN boot initiators correspondingly. Moreover, I have another pair of vHBAs (FC_2 and FC_3) that are to be used to connect to the SAN (not for SAN boot). This is a necessary requirement for proper LUN masking on the EMC VNX.
Highlight the newly created primary SAN boot initiator and select "Add SAN Boot Target". Type in the boot target LUN id and WWPN for the primary boot target. Repeat this for the secondary boot target. Once done, repeat all the steps above for the secondary SAN boot initiator. It should look something like this:
Note: FC_0 is pinned onto Fabric A which is physically connected to Storage Processors A Port 0 (SPA0) and SPB0 while FC_1 is pinned onto Fabric B which is physically connected to SPA1 and SPB1. Therefore, the primary and secondary WWPNs are configured correspondingly.
Once the settings have been applied, the UCS servers will now boot from SAN (assuming all the fiber channel zoning and LUN masking is configured).
If you have an EMC VNX storage on the back end, you may want to read here on how to configure the storage groups and LUN masking.