There is always a top-level default subvolume that is mounted by default, and all of its subvolumes. We can create subvolumes as easily as creating new directories, and can have nested subvolumes just like having sub-directories inside of directories. Subvolumes don’t have a fixed size, but are allocated space dynamically from the storage pool as data are added and removed. This is an ingenious construct that lets us easily create and manage a Btrfs storage pool all full of subvolumes that we can mount and unmount independently like block devices, but without hassling with disk partitioning. A Btrfs subvolume behaves somewhat like a block device, though it is not a block device but rather separate a POSIX file namespace. One of Btrfs’ coolest and most useful features is subvolumes. If you make a mess, for example a botched upgrade, this is a great way to keep your system up while you figure out what to do. But it’s a great tool for quickly going back in time to a known good state. Now we’re going to learn how to make live snapshots whenever we want, and how to roll the filesystem back to any point to any arbitrary point in time.

In “ How to Manage Btrfs Storage Pools, Subvolumes And Snapshots on Linux (part 1)” we learned how to create a nice little Btrfs test lab, and how to create a Btrfs storage volume.

Snapshot drive