B810n and the illusive 2.5 SSD caddy

I have the B810n and would like to switch over to SSD drives. The information Drobo published seems contradictory to me. Here B810n is states " Drives and Expansion; Up to 8 SATA or solid state drives (SSDs) or up to 3 SSDs". So which is it? 8 SATA SSD or 3? I’m confused by this statement.

Also, where do we buy the 2.5 caddy? I’d imagine it has to be specific to the Drobo?