Comment 18 for bug 251164

The udev rules don't need to prompt, the cryptsetup that gets called will prompt. Actually, these things work quite well in the normal system. It seems preferable to me to adjust/improve the regular tools to be usable in initramfs as well, rather then trying to script up and maintain! another thing inherently limited.

Failure hooks for example will be called in a specific order (not necessarily matching the setup), if you are looping this should time out with a message, then if the user plugs in the missing disk it won't come up automatically (and if it does possibly only with a large delay as all unrelated loops need to time out first), etc. Thus, its better to go event driven, and then why not favor a proven tool.

Reasonable timeouts (see above and https://wiki.ubuntu.com/ReliableRaid) are another reason to go event driven, they should not be several waiting loops stacked up and possibly blocking each other.

Bug #491463 "support upstart within an initramfs"
https://launchpad.net/~csurbhi/+archive/natty-initramfs