Selfhosted

From my point of view, you have two separate things.

First, you have a "business"/user case, you need a way for people to sync data with you. For this, it's a solved problem. Use Nextcloud/Owncloud/something with an app and a decent user experience for this. Whatever you like. On your primary "home" location, set this up, and have people start syncing data to you.

Second is the underlying storage. For this, again it's up to you, but personally I'd have a large NAS at home (encrypted), which is sync'd either in realtime or nightly (using something like cron/rclone) to the other locations (also encrypted, so not even they can see it).

Their portal to this data storage is the nice user experience like Nextcloud. They don't have to worry about how data is synced or managed. Nextcloud also supports quotas so you can specify how much they all get (so you don't have to deal with partitioning).

This approach will be much less headache for you. I think I understand what you're asking, where your original thought was just a dump of storage that is separate, but I think this is a better approach - both in terms of your sanity maintaining it and also their own usability.

Your requirements are really unclear.

• how many houses
• how far are they apart (latency)
• what is their internet connection like? up/downstream? Static IP? Is it stable?
• how are they supposed to access the data?
• what kind of data is it, and what is the access pattern? Meaning, is it text files? Occasional pictures? Movies?
• how much data do you need in total (yours+others)

one nas device with a lot of power and a vpn for the other houses might be better.

I'll share my experience with my very unprofessional but working setup.

I have two locations, both using retired PCs. I don't need anything fancy, but some considerations could be GPU/encoding hardware if you wanted something like jellyfin/Plex. I use proxmox and proxmox backup server for managing everything and so far it's been working well. Definitely not plug and play like an aio nas but that's because a nas wasn't my only goal as I needed cameras (frigate) and homeassistant.

I would highly recommend headscale/tailscale (as others have suggested) as it "just works" when setup in my experience. This enables safe remote access without opening any ports on your families networks so you can troubleshoot if something did break.

Regardless of which solution you decide to use, the most important part about having a backup is testing. If you can't see when your backups fail or don't know how to recover you may as well not have a backup.

I have a Synology nas. They recently started thumbing their nose at budget/home users and if I had to buy new I’d consider QNap.

I would set up a nas at each location and enable quick connect.

I would set up a redundant drive pool and create volumes to avoid single drive failure.

I would set up the Drive services. This works just like Dropbox or onedrive. I believe there’s a component that allows Drive on one NAS to sync with Drive on another.

I would set up hyperbackup between the NAS and use Tailscale to avoid playing with firewalls, dns, NAT.

Advanced I would set up federated authentication between the nas.

I would set up firewalls and dns.

Clients I would set up the photos mobile app for everyone.

I would set up google/onedrive backups.

I would set up the Drive app on their machines.

I strongly recommend ZFS as a filesystem for this as it can handle your sync, backup, and quota needs very well. It also has data integrity guarantees that should frankly be table stakes in this application. Truenas is an easy way to accomplish this, and it can run docker containers and VMs if you like.

Tailscale is a great way to connect them all, and connect to your nas when you aren’t home. You can share devices between tailnets, so you don’t all have to be on the same Tailscale account.

I’ll caution against nextcloud, it has a zillion features but in my experience it isn’t actually that good at syncing files. It’s complicated to set up, complicated to maintain, and there are frequent bugs. Consider just using SMB file sharing (built into truenas), or an application that only syncs files without trying to be an entire office suite as well.

For your drive layouts, I’d go with big drives in a mirror. This keeps your power and physical space requirements low. If you want, ZFS can also transparently put metadata and small files on SSDs for better latency and less drive thrashing. (These should also be mirrored.) Do not add an L2ARC drive, it is rarely helpful.

The boxes are kinda up to you. Avoid USB enclosures if at all possible. Truenas can be installed on most prebuilt NAS boxes other than synology, presuming it meets the requirements. You can also build your own. Hot swap is nice, and a must-have if you need normies to work on it. Label the drive serial number on the outside so you can tell them apart. Don’t go for less than 4 bays, and more is better even if you don’t need them yet. You want as much RAM as feasibly possible; ZFS uses it for caching, and it gives you room to run containers and VMs.

I want to write this in a separate post because I see many questionable suggestions:

Your scenario does not allow for a simple rsync / ZFS copy. That is because those only work with 1:many. Meaning one "true" copy that gets replicated a couple of times.

As I understand you have a many:many scenario, where any location can access and upload new data. So if you have two locations that changed the same file that day, what do you do? many:many data storage is a hard problem. Because of this a simple solution unfortunately won't work. There is a lot of research that has gone into this for hyperscalers such as AWS GCP, Azure etc. They all basically came to the same solution, which is that they use distributed quorum based storage systems with a unified interface. Meaning everyone accesses the "same" interface and under the hood the data gets replicated 3 times. So it turns it back into a 1:many basically, with the advantages of many:many.

If I understood you correctly then you want each NAS to have two storage pools.

Pool1

• bigger pool
• only your data
• part of a distributed storage across all NAS(?)
• backup 3-2-1

Pool2

• smaller pool
• shared to the home network it is a part of
• backup 3-2-1

Is this correct?

I would probably go with a simple approach like this:

• ZFS: Each house gets a "NAS" that provides a ZFS filesystem to store the data. This gives you the ability to share the drives across your use cases (you, rest of the family), snapshots, RAIDZ support, and usage quotas. For the OS, you could use what you prefer (TrueNAS, Debian, Ubuntu, ...).
• Syncthing to synchronize the files across the servers/houses. This allows you to read and write data from anywhere and syncthing will mirror the writes to the other places. I use it to synchronize data across 5 devices and it works quite well.

There are probably more advanced (enterprise?) ways to handle the file synchronization. But, I think this hould be good enough for normal, personal use. The main disadvantage is that you're only synchronizing the current data (excluding the ZFS snapshots). On the other hand, this also allows you to mix file systems if necessary.

Put them all on the same tailscale/netbird metwork and use restic to encrypted backup from each one to the others. Each hpuse gwts their files from there own box and has encrypted backups to pull from if their unit fails

It's possible there is dedicate system to do this, I haven't researched it. But if not setting up syncthing would work. And if its a lot of data sync it local first then mail or drive the remote drive to them.

I really wish NAS discussions had their own community.