The OWC Mercury Elite-AL Pro Qx2 is for someone who needs a RAID unit with older interfaces, including FireWire 800 and eSATA.
This unit comes with a power supply and a key for the cabinet, but no hard drives. It is older and I believe it can only utilize hard drives up to 3 TB. Check with OWC (macsales.com) and they may be able to confirm. I used it for years in a hardware RAID 5 configuration with four 3TB drives installed. It worked just fine when I last tested it in February 2024.
The OWC Mercury Elite-AL Pro Qx2 is built for demanding performance-intensive applications such as Audio/Video editing, HD-video, digital photography, professional music, graphics, redundant backup, and any use requiring data storage performance and reliability. Pre-configured in a Hardware RAID 5 mode to provide data redundancy toensure uninterrupted access to stored data, as well as protecting against data loss,the Mercury Elite-AL Pro Qx2 can also be configured to automatically perform one of the otherthree hardware RAID settings: 0, 1, or 10, as well as a Span (NRAID) setting.Selecting and/or visually confirming the RAID setting is performed via a recessed selector switchsafely located behind the lockable front panel.

Plug & Play Desktop RAID For Mac & PC
The OWC Mercury Elite-AL Pro Qx2 also offers a variety of convenience features that make adding it to any Mac or PC Plug & Play easy:FireWire 800, FireWire 400, USB 2.0, and eSATA interfaces,along with connection cables, provide compatibility with multiple operating systems and computers;front panel LEDsgive quick, at-a-glance system status; and aremovable key lockensures the installed hard drives and selected RAID mode remain secure.