Connection protocols to enable external drives to connect to late 2015 27-inch iMac
I’m a big fan of using a dock or enclosure to reliably connect drives rather than chaining them. Cable chains can be safe and secure and work well, but I prefer one cable and hard mounting the drives:


https://eshop.macsales.com/item/OWC/TB2U3DKR2/


Most basic enclosures work in JBOD mode since you don’t usually want to RAID / mirror less than 5 drives or without a nice controller for most uses.