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mdadm: no devices found for /dev/md0

I've got a raid5 array on four disks, but when I try to reconstruct the array it fails as follows:

Code:

mdadm -A /dev/md0

mdadm: no devices found for /dev/md0

However, if I do

Code:

mdadm -A /dev/md0 /dev/hd[abef]1

then it reconstructs the array properly and you can see the results:

Code:

mdadm --detail --scan

ARRAY /dev/md0 level=raid5 num-devices=4 UUID=feebae85:4c152e6d:e63ff723:9401b138

  devices=/dev/hda1,/dev/hdb1,/dev/hde1,/dev/hdf1

Code:

mdadm --detail /dev/md0

/dev/md0:

        Version : 00.90.00

  Creation Time : Mon May 22 22:37:50 2006

    Raid Level : raid5

    Array Size : 468864768 (447.14 GiB 480.12 GB)

    Device Size : 156288256 (149.05 GiB 160.04 GB)

  Raid Devices : 4

  Total Devices : 4

Preferred Minor : 0

    Persistence : Superblock is persistent



    Update Time : Sun Jun 18 23:51:01 2006

          State : active

 Active Devices : 4

Working Devices : 4

 Failed Devices : 0

  Spare Devices : 0



        Layout : left-symmetric

    Chunk Size : 64K



          UUID : feebae85:4c152e6d:e63ff723:9401b138

        Events : 0.13



    Number  Major  Minor  RaidDevice State

      0      3        1        0      active sync  /dev/hda1

      1      3      65        1      active sync  /dev/hdb1

      2      33        1        2      active sync  /dev/hde1

      3      33      65        3      active sync  /dev/hdf1

The proper details for /dev/md0 are in /etc/mdadm/mdadm.conf and I've tried to remake this file from the working array by doing

Code:

mdadm -A /dev/md0 /dev/hd[abef]1

mdadm --detail --scan > /etc/mdadm/mdadm.conf

But then trying to reassemble the array the easy way still fails

Code:

mdadm -A /dev/md0

mdadm: no devices found for /dev/md0

???

I don't understand why this doesn't work, it used to...

I am almost sure for that if you open /etc/mdadm.conf you will not see the line for this raid array.
You have to add it to this config file and then have to enjoy.
I don't know why but mdadm doesn't write the configuration to the /etc/mdadm.conf. I had the same situation like you.
Just added the config lines to the file and then restart or just restart rc.d script.
In the /etc/mdadm.conf you have to add something like that:
ARRAY /dev/md0 level=raid0 UUID=ghjhg34:23423DFds:23423sdfa:234234fsSDF

Something like that. The UUID you will take with this command : mdadm --detail /dev/raid-device.

At last you have to enjoy your new raid array. :)

well, actually, that line for ARRAY is done by mdadm --detail --scan. What I forgot was the DEVICE /dev/hda1 /dev/hdb1... line before that. It works now.