Snapshots of 2 Hard Drives?

[PhysicistSarah]

So I now have 2 hard drives with content on them.

What is the best way to snapshot both of them. I previously had a master Snapshots folder which contained 2 folders "Home" and "Sarah". I tried adding a third folder of my other hard drive name, but got an invalid cross-device-link error.

Does each hard drive have to manage it's own snapshots? Or is there any way to keep the same idea of what I'm doing now?

[jlittle]

Each file system has it's own snapshots (remember, they're nearly instant). You've set up two file systems on different drives, and that might be the right for your uses, but you could have added the second drive to the btrfs on the first. There's a bunch of considerations, like how much redundancy you want.

If you want a snapshot of one fs on the other, you use btrfs send and receive, and the first time takes a while, as all the data have to be copied.

[PhysicistSarah]

I just updated my backup script that I use to take snapshots of both drives and put store them on the respective drive that they originated from

[oshunluvr]

In the BTRFS world, a "snapshot" only exists on the same file system as the source subvolume. A "backup" is a snapshot that has been relocated to a different file system. But there's very little advantage in having a "backup" on the drive as the source, because it's functionally the same as a snapshot. If the drive dies, so does your snapshots and backups on that drive.

A more logical setup would be to have the backups on a different drive, so if you have two drives with two BTRFS file systems on them, put the backups on the other drive. Snapshots, by definition, must be on the same file system.