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6.6. Backing Stores
LXC supports several backing stores for container root filesystems. The default is a simple directory backing store, because it requires no prior host customization, so long as the underlying filesystem is large enough.
It also requires no root privilege to create the backing store, so that it is seamless for unprivileged use. The rootfs for a privileged directory backed container is located (by default) under /var/lib/lxc/C1/rootfs, while the rootfs for an unprivileged container is under ~/.local/share/lxc/C1/rootfs. If a custom lxcpath is specified in lxc.system.com, then the container rootfs will be under $lxcpath/C1/rootfs.
A snapshot clone C2 of a directory backed container C1 becomes an overlayfs backed container, with a rootfs called overlayfs:/var/lib/lxc/C1/rootfs:/var/lib/lxc/C2/delta0. Other backing store types include loop, btrfs, LVM and zfs.
A btrfs backed container mostly looks like a directory backed container, with its root filesystem in the same location. However, the root filesystem comprises a subvolume, so that a snapshot clone is created using a subvolume snapshot.
The root filesystem for an LVM backed container can be any separate LV. The default VG name can be specified in lxc.conf. The filesystem type and size are configurable per-container using lxc-create.
The rootfs for a zfs backed container is a separate zfs filesystem, mounted under the traditional /var/ lib/lxc/C1/rootfs location. The zfsroot can be specified at lxc-create, and a default can be specified in lxc.system.conf.
More information on creating containers with the various backing stores can be found in the lxc-create manual page.