The new Mac Pro is a computing monster with two slots for SSD modules with the Promise expansions you can also get mechanical hard drives housed.

Promise Pegasus R4i

Promise, in collaboration with Apple, has introduced two extensions that bring either four or two 3.5″ hard drives into the new Mac Pro. This one has enough slots and the Pegasus R4i module fits into exactly one of the new MPX slots. It is preconfigured as RAID 5.

Promise Pegasus J2i

The smaller module should find room where Apple has left room for smaller PCIe cards. The module comes pre-configured by Promise with only one 8 TB disk, but can record a second one.