So instead of using a NAS as my primary bulk-data storage location, I decided to add bulk-storage to my Proxmox server itself.
The primary force behind this was that you can pick up 8 TB WD Easystores (external hard drives) for $130 each ($16.25 / TB). These external drives can be taken apart and the internal drive can be removed (process is informally known as “shucking”, like corn). The drive inside is typically a WD Red drive (with a generic, white label). WD Red is WD’s line of hard drives made for NAS devices.
I popped these into my Proxmox server, created a new zpool (mirror), and used zfs send/zfs receive to copy all my data from my FreeNAS box, to these drives. Now, I have a a large amount of storage, local to my Proxmox server and VMs/containers.
This also paves the way to repurpose my FreeNAS box. At a minimum, it will now solely be a backup destination.