I may have screwed up, I am not sure.
I have 5 750GB drives in a raid 5 array. The problem was that I forgot to set the part. type flag for each drive before building/adding/growing.
Only 2 of the drives had the flag set for raid. I thought if I faulted out one drive at a time I could correct this. Now I stuck.
I faulted out /dev/sda, ran cfdisk and set the flag to raid. There was no part. for the drive. I then removed /dev/sda from /dev/md0 and the added it back end. It seemed to be working and then the status kick out that /dev/sdd was set as faulty. Now --detail shows
/dev/md0:
Version : 00.90.03
Creation Time : Sun May 27 23:13:29 2007
Raid Level : raid5
Array Size : 2930297856 (2794.55 GiB 3000.63 GB)
Used Dev Size : 732574464 (698.64 GiB 750.16 GB)
Raid Devices : 5
Total Devices : 5
Preferred Minor : 0
Persistence : Superblock is persistent

Update Time : Sun Feb 24 08:45:31 2008
State : clean, degraded
Active Devices : 3
Working Devices : 5
Failed Devices : 0
Spare Devices : 2

Layout : left-symmetric
Chunk Size : 64K

UUID : 93e569e9:2ac62d3f:0604effb:113c2a70
Events : 0.695034

Number Major Minor RaidDevice State
0 0 0 0 removed
1 8 32 1 active sync /dev/sdc
2 8 16 2 active sync /dev/sdb
3 8 64 3 active sync /dev/sde
4 0 0 4 removed

5 8 48 - spare /dev/sdd
6 8 0 - spare /dev/sda


I then tried to remove /dev/sdd and add it back in.

Now --detail reports
mdadm: No md superblock detected on /dev/md0.
/dev/sdd:
Magic : a92b4efc
Version : 00.90.00
UUID : 93e569e9:2ac62d3f:0604effb:113c2a70
Creation Time : Sun May 27 23:13:29 2007
Raid Level : raid5
Used Dev Size : 732574464 (698.64 GiB 750.16 GB)
Array Size : 2930297856 (2794.55 GiB 3000.63 GB)
Raid Devices : 5
Total Devices : 5
Preferred Minor : 0

Update Time : Sun Feb 24 08:49:05 2008
State : clean
Active Devices : 3
Working Devices : 5
Failed Devices : 1
Spare Devices : 2
Checksum : 38f42a05 - correct
Events : 0.695038

Layout : left-symmetric
Chunk Size : 64K

Number Major Minor RaidDevice State
this 5 8 48 5 spare /dev/sdd

0 0 0 0 0 removed
1 1 8 32 1 active sync /dev/sdc
2 2 8 16 2 active sync /dev/sdb
3 3 8 64 3 active sync /dev/sde
4 4 0 0 4 faulty removed
5 5 8 48 5 spare /dev/sdd
6 6 8 0 6 spare /dev/sda


Any help?