Question: I have an HP Proliant DL 360 G6. ESXi is installed on the array controlled by the on board RAID controller (P420 I think)

ESXi recognizes the P812 RAID controller but when I put PCI passthrough on it I get a purple screen of death.

My goal is to virtualize an FTP/SAMBA server and give the P812 RAID controller (all 12TB of the MSA60) solely to the FTP/SAMBA VM and nothing else.

I have tried ESXi 5.1 (known to have broken PCI passthrough) and 5.0 (shouldn't have broken passthrough). How do I get this working?

Answer: 
Why would want to implement the complexity of passing it through. Just configure a datastore and present a VMDK or RDM only to your FTP/SAMBA server. This gives you may more flexibility and will be far more supportable. 

That said, by doing this anyway, you're losing a lot of the benefits of virtualisation unless you're going to implement some kind of replication system.
I know this post is a few years old, but I think he may have been interested in doing something similar to what I'm planning to do. I have an ESXi 5.5 host (DL380 G6 in fact) running a few essential VMs. The main datastore is supported by the Smart Array P400 ("on-board"). I have an external enclosure (MSA60) that connects directly to the Smart Array P812 (PCI) via Mini SAS cable. The hope is to cut equipment and operation costs by virtualizing a (currently physical) file server. Now, I do see where you are coming from with your recommendation to create another datastore and present it to the VM (in this case the file server), however, WS2012 includes some pretty fancy data management tools. Since I anticipate our storage needs growing over the next few years, I would like to be able to take full advantage of WS2012's Storage Spaces and Pools features.