If that question was directed at me: those are Sonnet Tempo Pro Plus cards. Each one hosts a pair of 2.5" SATA SSDs, and has ports for an external ESATA dock or enclosure. They are absolutely vintage now, but at one time (before NVME) they were about the best way to get relatively speedy drives into a CMP.
Right now, each of them hold 2 TB drives. When I built this machine in 2012 I needed to move multi-GB image files around (technical image analysis using Gimp). They were so much better than any spinners. And they lived much, much longer than the equally-vintage OWC Mercury Accelsior/Accelsior E2s, several of which died dramatically and expensively while in my possession... Now, I do everything active on the 4x 2TB NVME drives, and keep the Sonnets around as semi-speedy backup drives, backing up nightly (with CCC). I then back up the backups onto spinners via a desktop ESATA dock weekly, and rotate the set of spinners offsite to my safe deposit box monthly after a final full clone.
The best spinner I have does about 95MB/s on Blackmagic, the Sonnets do about 500, the Accelsiors did about 700 (for the few months they lasted, anyway), and the NVME does about 4500 in Raid 0-2 for my data drive. Needless to say, backing all that stuff up to spinners is an overnight activity at the first of the month...
We had a house fire a year ago, and the machine actually *survived* it- but ya gotta believe that I was still really glad that I had the offsite storage. I also wasn't too annoyed that the remaining stack of dead Accelsiors in my spares box got fricasseed along with the rest of the house: the fragility of those never-to-be-sufficiently-damned proprietary Sandforce SSD blades they used have been discussed here at length. Anybody who might wonder why I use such an overkill belt/suspenders/duct tape/superglue backup scheme with SSDs: there's your answer...