OpenMediaVault VS Syncloud

You might want to consider the previously mentioned MergerFS and SnapRAID, or MDADM and LVM for your setup. OpenMediaVault [https://www.openmediavault.org/ is a solid choice in this regard. Additionally, if you're planning to run something like Proxmox, you could look into deploying Starwind CVM on top of it. Pretty much like in this guide: https://www.starwindsoftware.com/resource-library/starwind-virtual-san-vsan-configuration-guide-for-proxmox-vsan-deployed-as-a-controller-virtual-machine-cvm/ .

You would better to install OMV instead. It's a ready to use fileserver solution with web interface.

So I'm working on a similar setup with an ancient desktop my in-laws were getting rid of. I installed OpenMediaVault directly to the hard drive (it's so old that I assume it wouldn't work too well as a hypervisor), with a 4TB external HDD attached. OMV supports Docker by means of a plug-in and I'm running a Jellyfin container with no issues at all. I'm still manually downloading everything to the HDD but *arr containers are my next step, as well as setting up a gluetun container to route all that through a VPN.

That is possible (it's automated to a certain extent). It also depends on the NAS OS. Unraid, for example, can work with drives of different sizes while using the largest one for parity. TrueNAS uses ZFS so you won't be able to just add a drive to your RAIDZ and expand it. There's also openmediavault: https://www.openmediavault.org/ that uses Linux Software RAID and you can add a new drive there but you can't combine drives of different sizes. And there's also Starwinds NAS that supports both Linux Software RAID and ZFS: https://www.starwindsoftware.com/san-and-nas. Plus, I would avoid SMR drives in RAID: https://nascompares.com/answer/list-of-wd-cmr-and-smr-hard-drives-hdd/

I'd put it like that: if you have a spare PC, then it's definitely worth trying. I would also look into openmediavault (minimal RAM needs): https://www.openmediavault.org/ and Starwinds NAS (supports both ZFS and Linux software RAID): https://www.starwindsoftware.com/san-and-nas

Your current PC looks very decent for a lab. Proxmox on it, then one Linux VM with Docker, another VM for NAS with something lite and easy like openmediavault: https://www.openmediavault.org/ or Starwinds NAS: https://www.starwindsoftware.com/san-and-nas and Plex separately. And other stuff in VMs or containers.

I was a helm user. Unfortunately, the helm went bellyup in December 2022. However, the nextcloud sofrware coupled with the helm/home server solution worked well. I am interested home solution, for sharing files. I am considering HomeDrive or the other solutions proposed on the nexcloud website (https://nextcloud.com/devices/) . I am wondering if there has been any successes or failures with HomeDrive N7 or similar device that suppors nextcloud, for a home server. I researched reddit and found folks recommending syncloud.org, however, as of 4/29/23 at 10:32 AM PST there severs are not available to me for some reason or another.

If you do not trust the cloud, there are managed self-hosting options where you can host your nextcloud physically at home, like using nextcloudpi, HomeDrive or Syncloud, where you only need to trust their software update to keep the system secure and to not plant a back door Some are also open source, so in theory you can even audit and build the software by yourself. In the worst case, when you feel that your data is in danger, you have the option to physically unplug your data off the network. For this kind of self-hosting at your own place, remember to at least properly get a valid TLS/HTTPS certificate.