St. Purple,
If you installed a SME 6.x standard Raid 1 (?), you should have used the pair of drives called hda and hdc.
/dev/hdb ...indeed doesn't have any part in all of that.
Why not post your INITIAL error message that tells what disk went wrong,
then describe WHAT (faq) you used in more detail and
WHEN you get that error message you posted.
...my crystal ball isn't clear enough to assume all that data and give a useful answer...
At least give us your raidtab and possibly the result old that cat /proc/mdstat ...message
