Editing Openai/695158d7-1b68-800b-a02f-4817bf1f6d25 (section)

=== Short: there’s no “two filesystems in the same partition” magical thing — you can only have one filesystem occupying a partition. But the terms you see are talking about two different layered concepts: ===
* btrfs partition (what you pick in the partition editor): you create a partition on disk and format it with the btrfs filesystem. That means the whole partition is a btrfs filesystem.
* btrfs volume / subvolume (internal to btrfs): inside a btrfs filesystem you create subvolumes (sometimes shown as “volumes” in GUIs). Subvolumes act like independent mountable roots but they live inside the single btrfs filesystem (they are not separate partitions). btrfs also supports multiple devices combined into a btrfs pool, RAID levels, etc.

So:
* If the GUI shows both options for the same slice of disk, it likely means (a) create a partition and (b) create a btrfs filesystem on it and then optionally create subvolumes inside it. You cannot have a separate ext4 and btrfs both on the same partition — you must pick one filesystem per partition.

If you want LVM + encryption, that’s a different model: LVM gives you logical volumes (LVs) that look like separate block devices and you can format each LV with ext4 / btrfs etc. btrfs subvolumes are more akin to directories with special semantics, not block-device LVs.