1) look at your syslog / dmesg to see what auto-detection and initial
tries by your configuration said.
2) You probably want something like I keep as a backup in my
initrd/initramfs images:

/sbin/mdadm --examine --scan /dev/[sh]d* /dev/mapper/* >
/etc/mdadm.conf.OR.SOME.FILE
/sbin/mdadm --assemble --scan --no-degraded
--config=/etc/mdadm.conf.OR.SOME.FILE

If you drop the .OR.SOME.FILE you don't need to specify a non-default
config.  You also don't need to specify any config if you explicitly
name your devices: I'm asking mdadm to examine every block device (and
partition on such) that I think even possibly could be a raid member.