If you want to play in that space you'll have to go with external solutions, there's no internal controllers that can do what you want, the reason being that most of these setups require multipath FCAL connections.
First you'll have to look at your RAID head units, your choices include Netapp, EMC, HP, Hitachi, Sun and then you get into the esoteric stuff like 3PAR, Ibrix + SAN and other more over the top solutions. Those will all do multicontroller scenarios, x2 or x4 or even bigger. Then you have to have your matrix, this includes switches from Brocade or Cisco, or some other vendor to tie in your FCAL matrix, if you want to be truly redundant you'll have to have ACTIVE/ACTIVE or ACTIVE/STANDBY for the switches too, so you'll need two of them. SAS was supposed to provide dual path controllers to every disk but currently there are no dual controller SAS solutions on the market yet. -DK
