Removing an unwanted RAID 1 array

[Roger Price <debian@rogerprice.org>]

I am unable to erase an unwanted RAID 1 array.  Command cat /proc/mdstat reported 

 md4 : active raid1 sdb7[0]
       20970368 blocks super 1.0 [2/1] [U_]
       bitmap: 1/1 pages [4KB], 65536KB chunk

I understand that the array has to be inactive before it can be removed, so I 
stopped it, but was not able to remove the array

 root@titan ~ umount /dev/md4
 root@titan ~ mdadm --misc /dev/md4 --stop
 root@titan ~ mdadm --manage /dev/md4 --remove /dev/sdb7
 mdadm: hot remove failed for /dev/sdb7: Device or resource busy

The command ps -ef | grep md4 reports

 root   211  2  0 Jan09 ? 00:00:00 [md4_raid1]

I assume process 211 is keeping md4 busy.  Do I have to kill process 211 or is 
there some more elegant way?  Or is it mdadm itself in process 663 which is 
keeping md4 busy?

 root   663  1  0 Jan09 ? 00:00:00 /sbin/mdadm --monitor --scan

The documentation I have found shows lots of examples of building RAID 1 arrays, 
but not removing them.  The program mdadm does not have a --disassemble mode. 
Any suggestion would be much appreciated.

Roger