The D2600/2700 has dual 6Gbps SAS channels on the backplane, the cables you connect them with carry four x 6Gbps SAS channels to allow you to daisy-chain another shelf off the first one without any port blocking when connected to a four channel card such as a P812/822.
By the way if I were you I'd simply create one large RAID 10 array and then create the number of logical disks you need from that array - it'll perform far better than the R1+R1+R10 suggestion. Come back to us if you have further queries, this is right up my alley ;)