Getting desperate here now.
purchased refurbished ps6510e from third party reseller - have been flatly refused access to dell's site for support based on that.
got it connected to 2 R720 servers via teamed 10gb SFP+ cables through an 8024F switch to SAN with redundant 10gb connections on dual controllers. configured on private network for iscsi traffic only with private addresses for each of the servers, switch, san individual nics and san group ip.
configured corporate / management network for servers / san / switch management with works perfectly.
the 2 servers (2012r2) can communicate between each other via the 20gb links. no communication with san via ping or linking iscsi connectors at all. servers can ping each other and switch, not san. CLI to san - cant ping anything - not even its own individual ip addresses. SAN web interface reports which switch ports (15+16) it is plugged into on the switch so it knows it exists and is connecting to it seemingly happily.
switch configured according to guidelines from dell white papers, jumbo frames, LAG's. I have swapped 10gb connections between servers and san groups, and whichever combination of connections, servers talk, san doesn't.
web interface and SAN HQ all report everything to be hunky dory. only error is about free space as we have provisioned volumes to take up everything.
any bright ideas as to what has gone fundamentally wrong most welcomed.