E6600-24XG - Distributed Trunking and STP question

[Tom Bunton]

I haven't seen a posting about this particular scenario yet (which may mean I haven't looked hard enough!), so...

I have 2 E6600-24XG switches I use for vSphere iSCSI connectivity to our HP Lefthand SAN.  Both switches are connected to a 10Gb module in a 5412zl, one SFP+ cable per 6600, to communicate to each other, and to allow the SAN to communication with another Lefthand SAN at a remote site.

A couple of years ago, when I originally setup these switches, I had turned on spanning tree, then turned it back off a few months later, as it wasn't needed, and was knocking the LH SAN ports off for 2 seconds when a SAN node was rebooted.

I want to setup a distributed trunk for a 3rd party NAS we're going to use for B2D.  Which also means I have to designate a switch-interconnect port.

Currently the 10Gb interfaces in each Lefthand SAN node is configured in ALB mode, and appear to be working OK without distributed trunking.  I believe the Thecus NAS we're going to use for B2D requires DT to use ALB.

Question:  Can I designate the already in use uplinks to the 5412 as the switch-interconnect on each 6600?  Or do I need to use a completely separate port and connect 6600 directly to 6600?

Question:  If I have to connect 6600 directly to 6600, will I have to turn on spanning tree again?  Will there be any interruption in my iSCSI traffic to/from the Lefthand SANs?  Will there be any disruption on the rest of my network?

Question(last one for now!):  If I have to use direct 6600 to 6600 interconnect, do I need to do anything special with the uplinks to the 5412?  Keepalive VLAN?  Priority???

Thanks in advance, everyone!