Dell PowerEdge T420 storage expansion options?

Hi all.

I recently bought a used Dell PowerEdge T420 server.

It’s configured with 8 x 3.5" hot swappable bays. It also came with a Perc H710 that I’ve flashed into IT mode and I currently have all the 3.5" drives configured using ZFS for storing my Proxmox Virtual Machines.

Ideally, I want a fast storage pool I can store my virtual machines on, and I’m trying to figure out what my options are. My server is configured with x2 Xeon E2420 CPU’s and 64B ECC DDR3.

I have two 5.25” bays available to use if needed.

I’ve been trying to do some research, but the options are overwhelming.

What options do I have for creating a storage pool that is very fast, uses ZFS, and can be used within Proxmox?