[mythtv-users] RAID: full disk or partition (was: Question re: available SATA ports and linux software RAID)

[Jean-Yves Avenard]

I'm having a bit of troubles as mdadm doesn't survive a reboot (e.g.
it doesn't restart the RAID)

I can start md manually with:
root at htpc:~# mdadm -ARs
mdadm: superblock on /dev/sdd doesn't match others - assembly aborted
mdadm: superblock on /dev/sdd doesn't match others - assembly aborted
/dev/md0: File exists
mdadm: /dev/md/0 has been started with 5 drives.

root at htpc:/data# sudo mdadm --detail /dev/md0
/dev/md0:
        Version : 00.90
  Creation Time : Sat Apr  4 02:32:09 2009
     Raid Level : raid5
     Array Size : 7814047744 (7452.06 GiB 8001.58 GB)
  Used Dev Size : 1953511936 (1863.01 GiB 2000.40 GB)
   Raid Devices : 5
  Total Devices : 5
Preferred Minor : 0
    Persistence : Superblock is persistent

    Update Time : Wed Apr 27 11:47:55 2011
          State : clean
 Active Devices : 5
Working Devices : 5
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 128K

           UUID : c4da37ea:99c0fc03:a5e8058a:6a55fa23 (local to host
htpc.avenard.org)
         Events : 0.9720100

    Number   Major   Minor   RaidDevice State
       0       8       49        0      active sync   /dev/sdd1
       1       8       65        1      active sync   /dev/sde1
       2       8       33        2      active sync   /dev/sdc1
       3       8       81        3      active sync   /dev/sdf1
       4       8        1        4      active sync   /dev/sda1

---
The problem comes that I first added /dev/sdd as full disk ; I then
removed that disk and added it as a partition /dev/sdd1.
root at htpc:/data# mdadm --examine /dev/sdd
/dev/sdd:
          Magic : a92b4efc
        Version : 00.90.00
           UUID : c4da37ea:99c0fc03:a5e8058a:6a55fa23 (local to host
htpc.avenard.org)
  Creation Time : Sat Apr  4 02:32:09 2009
     Raid Level : raid5
  Used Dev Size : 1465135872 (1397.26 GiB 1500.30 GB)
     Array Size : 5860543488 (5589.05 GiB 6001.20 GB)
   Raid Devices : 5
  Total Devices : 5
Preferred Minor : 0

    Update Time : Mon Apr 25 14:27:10 2011
          State : clean
 Active Devices : 5
Working Devices : 5
 Failed Devices : 0
  Spare Devices : 0
       Checksum : 80dc4b5 - correct
         Events : 9696394

         Layout : left-symmetric
     Chunk Size : 128K

      Number   Major   Minor   RaidDevice State
this     0       8       48        0      active sync   /dev/sdd

   0     0       8       48        0      active sync   /dev/sdd
   1     1       8       64        1      active sync   /dev/sde
   2     2       8       33        2      active sync   /dev/sdc1
   3     3       8       80        3      active sync   /dev/sdf
   4     4       8        1        4      active sync   /dev/sda1

which is different than the superblock found in /dev/sdd1
root at htpc:/data# mdadm --examine /dev/sdd1
/dev/sdd1:
          Magic : a92b4efc
        Version : 00.90.00
           UUID : c4da37ea:99c0fc03:a5e8058a:6a55fa23 (local to host
htpc.avenard.org)
  Creation Time : Sat Apr  4 02:32:09 2009
     Raid Level : raid5
  Used Dev Size : 1953511936 (1863.01 GiB 2000.40 GB)
     Array Size : 7814047744 (7452.06 GiB 8001.58 GB)
   Raid Devices : 5
  Total Devices : 5
Preferred Minor : 0

    Update Time : Wed Apr 27 11:48:37 2011
          State : clean
 Active Devices : 5
Working Devices : 5
 Failed Devices : 0
  Spare Devices : 0
       Checksum : 252d02c4 - correct
         Events : 9720100

         Layout : left-symmetric
     Chunk Size : 128K

      Number   Major   Minor   RaidDevice State
this     0       8       49        0      active sync   /dev/sdd1

   0     0       8       49        0      active sync   /dev/sdd1
   1     1       8       65        1      active sync   /dev/sde1
   2     2       8       33        2      active sync   /dev/sdc1
   3     3       8       81        3      active sync   /dev/sdf1
   4     4       8        1        4      active sync   /dev/sda1

I tried zeroing the superblock, but it fails (that was before md was
started, so /dev/sdd shouldn't even have been in use)
root at htpc:~# mdadm --zero-superblock /dev/sdd
mdadm: Couldn't open /dev/sdd for write - not zeroing

Any ideas ?

Thanks
JY