Cannot create raid5 with 4 disks corectly

[Reiner Buehl <reiner@buehl.net>]

Hi all,

on my Debian Lenny system (with latest updates), I have the following 
problem:

I would like to create another RAID5 array consisting of 4 2TB disks. 
When creating the array with

    /sbin/mdadm --create --verbose /dev/md5 --level=5 --raid-devices=4 
/dev/sdm1 /dev/sdn1 /dev/sdo1 /dev/sdp1

the array is created but with one failed disk and a spare instead of 4 
working disks:

bilbo:~# mdadm --detail /dev/md5
/dev/md5:
        Version : 00.90
  Creation Time : Sat Dec  4 12:55:01 2010
     Raid Level : raid5
     Array Size : 5860540416 (5589.05 GiB 6001.19 GB)
  Used Dev Size : 1953513472 (1863.02 GiB 2000.40 GB)
   Raid Devices : 4
  Total Devices : 4
Preferred Minor : 5
    Persistence : Superblock is persistent

    Update Time : Sat Dec  4 12:55:01 2010
          State : clean, degraded
 Active Devices : 3
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 1

         Layout : left-symmetric
     Chunk Size : 64K

           UUID : cd14d406:2f66f930:ac80d277:73fa76dc (local to host 
bilbo.lan.buehl.net)
         Events : 0.1

    Number   Major   Minor   RaidDevice State
       0       8      193        0      active sync   /dev/sdm1
       1       8      209        1      active sync   /dev/sdn1
       2       8      225        2      active sync   /dev/sdo1
       3       0        0        3      removed

       4       8      241        -      spare   /dev/sdp1

The funny thing is, that this is not related to one disk: If I change 
the order of the devices in the mdadm command line, another device gets 
marked as spare instead of /dev/sdp1. It is always the device that was 
specified last in the mdadm --create command line.

dmesg shows no obvious errors and gives no hint, why one disk is not 
added and is treated as spare instead:

[ 5634.208141] md: bind<sdm1>
[ 5634.216134] md: bind<sdn1>
[ 5634.224044] md: bind<sdo1>
[ 5634.231632] md: bind<sdp1>
[ 5634.273202] raid5: device sdo1 operational as raid disk 2
[ 5634.273210] raid5: device sdn1 operational as raid disk 1
[ 5634.273214] raid5: device sdm1 operational as raid disk 0
[ 5634.273470] raid5: allocated 4222kB for md5
[ 5634.273555] 2: w=1 pa=0 pr=4 m=1 a=2 r=4 op1=0 op2=0
[ 5634.273557] 1: w=2 pa=0 pr=4 m=1 a=2 r=4 op1=0 op2=0
[ 5634.273558] 0: w=3 pa=0 pr=4 m=1 a=2 r=4 op1=0 op2=0
[ 5634.273560] raid5: raid level 5 set md5 active with 3 out of 4 
devices, algorithm 2
[ 5634.273562] RAID5 conf printout:
[ 5634.273563]  --- rd:4 wd:3
[ 5634.273564]  disk 0, o:1, dev:sdm1
[ 5634.273566]  disk 1, o:1, dev:sdn1
[ 5634.273567]  disk 2, o:1, dev:sdo1
[ 5634.273588] md5: detected capacity change from 0 to 6001193385984
[ 5634.275048]  md5: unknown partition table

Any ideas how I can fix this?

Regards,
Reiner Buehl.