Short report-back on this in the event it helps someone else. I added a HBA330 internal card. The few observations I have is; 1. As was stated above, it's needed to use a supported PCI slot (or else it wont be visible to VMware - this might be because I use single CPU but still). 2. Splitting the backplane works as expected - the HBA card gets the disks in the lower half and the H730p gets the disks in the upper (no surprise there). 3. I did try to just keep the backplane connected together and use one of the channels for the H730p and one for the HBA330 to see if I could utilise all disk-slots (single channel SAS would be fine for my use-case) - just keeping in mind what disks are used where. This caused the server to not boot (H730p initialised but I guess that caused issues for the HBA330). 4. The error which says the backplane is no connected did not go away from connecting to another card - its possible to mute it in the LC and configure the server to bypass it in boot but it will always be there which isn't very elegant.  To summarise - the best solution in my mind to run a virtual ZFS solution on a Dell tower server is to use 2 cards, 1 for boot (RAID) and one for ZFS appliance/server (HBA) connected to one backplane each. That gives 16 drives to the ZFS appliance (max) and will throw a (mutable) error. I know there are supported solutions (740XD with one card connected to flex-bays comes to mind) for this but for a home/office solution - the above is the best way forward I could figure out.
Hi, On my new T640 server I have 32 disk capable backplane (which consists of two 16 disk capable backplanes with a "patch" between them). I understand it was (probably) possible to buy it with multiple controllers but that was overlooked so there is a single H730 controller in it. I would now like to add another HBA card (dell compatible) in order to virtualise Freenas while retaining the H730 as a boot device and datastore (RAID:ed) for vmware. I don't want to just give Freenas access to a few of the drives (by running it in HBA mode) but to the entire HBA card connected to the lower backplane with 16 drives while using the H730 in RAID mode connected to the upper backplane.  The issue is I get a persistent warning on each boot (cbl0009) where the server cannot find the lower backplane as I've removed the "patch" between them to physically split them. I cant seem to figure out a way to shut that off, there is a "Enclosure configuration" named "BP14G+EXP 0:1" in idrac but that does not seem to be changeable. I want the server to boot up without warning on the single backplane - as its possible to order it with a single backplane I assume it can be done, but can it be changed after it was ordered?  
T640 split backplane for 2 controllers (cbl0009)