Promise Technology Pegasus R6 with 6 hard drives, 4TB each, set up as RAID5. This gives 20TB of storage, protected by the RAID5 configuration (hardware RAID) if one of the hard drives fails. It can also be set up as RAID0, which would give 24TB of storage. I have two of these units, $350 each. These have two Thunderbolt 2 connections, and can be daisy chained. Power cables and Thunderbolt 2 cables are supplied with the drives.