Is using Samba for 3000 users across two continents a good idea?

Using Samba might work, but it could be a hassle to manage for such a large user base. If you're in a Windows-centric environment, sticking with Microsoft's AD would save you a lot of potential issues. 3000 users relying on Samba could turn into a management nightmare.

Just a heads up, Samba can be a decent choice but is not built for a massive scale like you're talking about. If you're also considering features like roaming profiles or more advanced Windows application deployments, it's best to go for the full AD package.

Honestly, I'd recommend just going with Active Directory. If you're in a Windows environment, it can manage multiple domain controllers with ease, especially if you'd want to integrate with services like Microsoft Entra (formerly Azure AD). You can have low-spec Windows Server VMs that would do the job just fine without headaches.

While Samba offers a lightweight option for authentication, it has limitations, especially with Windows integrations. If you foresee needing features from Microsoft 365 or complex device management, don’t cut corners. Invest in a proper AD solution—it'll be worth it in the long run.

Samba can handle this scale, but there are some important caveats to keep in mind. For instance, Samba doesn't have built-in replication for domain repositories, which is where Group Policy Objects (GPOs) are stored. You'll have to set up some kind of sync mechanism like rsync. If your future plans don't involve complicated Microsoft-specific features, it should work well for authentication and file sharing. Plus, transitioning to a Microsoft AD server later isn't supposed to be overly complicated if needed.