What luks, lvm and mdadm layouts are bootable?

The only supported by default configuration layout is mdadm at the lowest
layer, then lvm and luks in any order.

(tested on Debian 8, initramfs-tools)

What luks, lvm and mdadm layouts are bootable?

The only supported by default configuration layout is mdadm at the lowest
layer, then lvm and luks in any order.

initramfs and noexec /tmp

If during creation of new initramfs by update-initramfs (called by e.g.
kernel postinst script) /tmp is mounted with 'noexec', initramfs will be
slightly different and may report errors, like

E: /scripts/local-premount/resume failed with return 255.