Connecting Thunderbolt 2 device to 2010 Mac Pro
You can connect the Promise Pegasus R4/R6 RAID directly to any 2013 Mac Pro.

You will need, however, a Thunderbolt 2 cable. These cables need to be bought separately and cost about about $35.

I have a Pegasus R4 RAID myself and can connect it to other Macs using the Thunderbolt cable without any issues. Keep in mind that you cannot connect two Macs simultaneously to the same Pegasus RAID.