On Wed, 26 Nov 2008 11:40:52 -0500, Greg Cormier wrote

I have a RAID5 array of 4 disks. Was working well. I did a "yum
update" and noticed it updated mdadm to mdadm 2.6.7.1, amongst other
things (new kernel 2.2.27 instead of .26) , and now my array won't
mount.

mdadm --assemble /dev/md0 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/sde1
mdadm: cannot open device /dev/sdb1: Device or resource busy
mdadm: /dev/sdb1 has no superblock - assembly aborted

[root@zeus ~]# cat /proc/mdstat
Personalities :
md_d0 : inactive sdb1[0](S) sdd1[2](S)
      976766976 blocks

unused devices: <none>

Did your md devices get renamed?
You are trying to assemble md0 but yet proc/mdstat shows md_d0
as the device name.