How to free devices held captive by failed arrays

[Harry Mangalam <hjm@moo.nac.uci.edu>]

(apologies if this is a repost - sent 3 attempts into the vger void already)

In doing some tests with an 8-port Supermicro/Marvell-based SATA controller
(works fine so far) and some Hitachi 3TB disks, I've run into an odd
problem.  One of the disks failed in burn-in, so the RAID5 went into
degraded mode.  In replacing the failed disk, I managed to bugger it up; not
so awful since it's a test rig and I needed to create 2 smaller arrays for
some testing. 


In trying to do that, I was able to create the first 4-disk RAID5 fine and
it's now initializing, but the second fails with the following error:


$ mdadm --create  --verbose /dev/md1 --level=5 --raid-devices=4
/dev/sd[fghi]1
mdadm: layout defaults to left-symmetric
mdadm: layout defaults to left-symmetric
mdadm: chunk size defaults to 512K
mdadm: /dev/sdf1 appears to be part of a raid array:
    level=raid5 devices=7 ctime=Fri Sep 30 17:47:19 2011
mdadm: layout defaults to left-symmetric
mdadm: super1.x cannot open /dev/sdg1: Device or resource busy
mdadm: /dev/sdg1 is not suitable for this array.
mdadm: layout defaults to left-symmetric
mdadm: /dev/sdh1 appears to be part of a raid array:
    level=raid5 devices=7 ctime=Fri Sep 30 17:47:19 2011
mdadm: layout defaults to left-symmetric
mdadm: create aborted


mdstat implies that one of the disks still belongs to the previous RAID5:


$ cat /proc/mdstat 
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4]
[raid10] 
md0 : active raid5 sde1[4] sdd1[2] sdc1[1] sdb1[0]
      6442438656 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/3]
[UUU_]
      [========>............]  recovery = 40.1% (861382528/2147479552)
finish=292.9min speed=73167K/sec
      
md_d0 : inactive sdg1[5](S)
      2147480704 blocks
       
unused devices: <none>




but I can't seem to convince md_d0 to surrender this device.  This behavior
survives a reboot.


One wrinkle is that the original RAID was made with the default mdadm from
Ubuntu 10.04.3 (2.6.7.1) and the smaller RAID5 above was created with the
latest mdadm (v3.2.2).  


What do I have to do to free this device?


TIA,


-- 
Harry Mangalam - Research Computing, OIT, Rm 225 MSTB, UC Irvine
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