I can’t answer each bullet (and a couple are dependant on other things like drive speed, activity, and network throughput) but I’ve been using shucked external HDDs for over a decade and would recommend it. I used to use OpenMediaVault running in a VM on Proxmox and briefly tried TrueNAS, but I’ve since migrated all of my VMs to LXCs, so now I just have the drives mounted on the Proxmox host directly combined with mergerfs (not managed by Proxmox’s storage pools) and I pass it through to a Turnkey Linux file server LXC via bind mounts to share over SMB/NFS. Less overhead and LXCs can share CPU/memory dynamically while VMs can’t.

You should be able to replace that /mnt/external directory with no issues as long as the structure is the same within.

My server itself is a little HP mini PC. i7, 2 TB SSD, solid little machine so far. Running Proxmox with a single debian VM which houses all my docker containers - I know I’m not using proxmox to its full advantage, but whatever it works for me. I mostly just use it for its backup system.

Not sure how mini you mean but if it has spots for your two drives this should be plenty of hardware for both NAS and your VMs. TrueNAS can run VMs as well, but it might be a pain migrating from Proxmox.

Think of Proxmox as a VM host that can do some NAS functions, and TrueNAS as a NAS that can do some VM functions. Play with them both, they will have their own strengths and weaknesses.

I’ve been reading about external drive shucking, since apparently that’s a thing? Seems like my best bet here would be to crack both of these external drives open and slap them into a NAS. 16TB would be plenty for my use.

It’s been a couple of years since I have shucked drives but occasionally the drives are slightly different than normal internal drives. There were some western digital drives that had one pin that was different from normal and worked in most computers, but some power supplies which had that pin wired required you to mask the pin before the drive would fire up.

I wouldn’t expect any major issues just saying you should research your particular model.

You say 16TB with two 8TB drives so I assume you aren’t expecting any redundancy here? Make sure you have some sort of backup plan because those drives will fail eventually, it’s just a matter of time.

You can build those as some sort of RAID0 to get you 16TB or you can just keep them as separate drives. Putting them in a RAID0 gives you some read and write performance boost, but in the event of a single drive failure you lose everything.

If 8TB is enough you want to put them in a mirror which give you 8TB of storage and allows a drive to fail without losing any data. There is still a read performance boost but maybe a slight loss on write performance.

Hardware: while I like the form factor of Synology/Terramaster/etc, seems like the better choice would be to just slap together my own mini-ITX build and throw TrueNAS on it. Easy enough, but what sort of specs should I look for? Since I already have 2 drives to slap in, I’d be looking to spend no more than $200. Alternatively, if I did want the convenience and form factor of a “traditional” NAS, is that reasonable within the budget? From what I’ve seen it’s mostly older models in that price range.

If you are planning on running Plex/Jellyfin an Intel with UHD 600 series or newer integrated graphics is the simplest and cheapest option. The UHD 600 series iGPU was the first Intel generation that has hardware decode for h265 so if you need to transcode Plex/Jellyfin will be able to read almost any source content and reencode it to h264 to stream. It won’t handle everything (i.e. AV1) but at that price range that is the best option.

I assume I can essentially just mount the NAS like an external drive on both the server and my desktop, is that how it works? For example, Jellyfin on my server is pointed to /mnt/external, could I just mount a NAS to that same directory instead of the USB drive and not have to change a thing on the configuration side?

Correct. Usually a NAS offers a couple of protocols. For Linux NFS is the typical filesystem used for that. For Windows it would be a Samba share. NFS isn’t the easiest to secure, so you will either end up with some IP ACLs or just allowing access to any machine on your internal network.

If you are keeping Proxmox in the mix you can also mount your NFS share as storage for Proxmox to create the virtual hard drives on. There are occasionally reasons to do this like if you want your NAS to be making snapshots of the VMs, or for security reasons, but generally adding the extra layers is going to cut down performance so mounting inside of the VM is better.

Will adding a NAS into the mix introduce any buffering/latency issues with Jellyfin and Navidrome?

Streaming apps will be reading ahead and so you shouldn’t notice any changes here. Library scans might take longer just because of the extra network latency and NAS filesystem layers, but that shouldn’t have any real effect on the end user experience.

What about emulation? I’m going to set up RomM pretty soon along with the web interface for older games, easy enough. But is streaming roms over a NAS even an option I should consider for anything past the Gamecube era?

Anything past GameCube era is probably large ISO files. Any game from a disk is going to be designed to load data from disk with loading screens, and an 8tb drive/1gb Ethernet is faster than most disks are going to be read. PS4 for example only reads disks at 24MB/s. Nintendo Switch cards aren’t exactly fast either so I don’t think they should be a concern.

It wouldn’t be enough for current gen consoles that expect NVMe storage, but it should be plenty fast for running roms right from your NAS.