Sysadmin

It depends on where you want to focus on protecting against ransomware. You can protect the NAS itself and you can focus on protecting network mount points hosted on the NAS. I would suggest planning for both since it’ll also protect you if your NAS dies/catches fire/etc.

To protect my home NAS itself from getting ransomwared, I use two external HDDs on a rotating basis stored in a safe. Every 6 months I plug the drive with the oldest backup into my NAS, overwrite the backup with the storage mount points I care about, print out a new label with the date, and put it in a safe. Ransomware can’t attack an unplugged drive.

If you’re a business or if the costs work out for you as a home user, you could just go cloud. Some cloud providers allow you to write to the store in an append-only manner. For example, Backblaze B2 lets you store data in a way where it won’t delete old data until after a certain amount of time passes. Depending on what you’re using to back up, you may be able to configure your NAS’s access to your cloud provider to only allow writes but not overwriting/deletes, or at least some form of file versioning.

To protect data from clients getting ransomwared, I turn on snapshots. With snapshots, if data gets written to your NAS, it’ll keep a copy of the old version of a file as well as the new version. You can restore snapshot’s fairly quickly because you just tell the file system to go back to the old versions. This gives you a near-instant way to restore data if a client becomes compromised and overwrites shared network storage. But note: this is not a replacement for a backup that is disconnected and offline

Some Synology devices let you turn on BTRFS snapshots and set a schedule for when they’re taken and when you want to clean them up. The issue is that this can “waste” a lot of space if you frequently change large files or add/delete large amounts of data. You will want to balance how often you create snapshots with how long you wish to retain the snapshots.

Using both of these mechanisms, I get the ability to quickly undo ransomware if my laptop gets hit and starts encrypting all of the data on its mounted network shares. If, for whatever reason, my NAS itself gets compromised, I’m only out 6 months of data. Could I back up more often? Sure, but my data doesn’t change that much anyways.