This is the state of the disk subsystem after rebooting from 10.04 live media an bringing up /dev/md0 on one disk (to make backups) and then re-adding the second disk to rebuild the array. Notice /dev/md0p1 is Gone and pvs says it's using /dev/md0 now!    



[08:06 06/13/13]
[root@usb-live /mnt/slash]
#  mdadm --readwrite /dev/md0

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  mdadm --add /dev/md0 /dev/sdc1
mdadm: re-added /dev/sdc1

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  cat /proc/mdstat 
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid1 sdc1[2] sdb1[0]
      58615552 blocks [2/1] [U_]
      [>....................]  recovery =  0.3% (198592/58615552) finish=14.7min speed=66197K/sec
      
unused devices: <none>

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  pvs
  PV         VG     Fmt  Attr PSize   PFree  
  /dev/md0   vgssd  lvm2 a-    55.90g  20.90g
  /dev/sda3  vgsata lvm2 a-   913.29g 824.29g

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  lvs
  LV        VG     Attr   LSize  Origin Snap%  Move Log Copy%  Convert
  home      vgsata -wi-a-  4.00g                                      
  mysql.bak vgsata -wi-a- 10.00g                                      
  sysbak    vgsata -wi-a- 50.00g                                      
  usr       vgsata -wi-ao  5.00g                                      
  var       vgsata -wi-ao 20.00g                                      
  mysqldump vgssd  -wi-a- 10.00g                                      
  usr       vgssd  -wi-ao  5.00g                                      
  var       vgssd  -wi-ao 20.00g                                      

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  vgs
  VG     #PV #LV #SN Attr   VSize   VFree  
  vgsata   1   5   0 wz--n- 913.29g 824.29g
  vgssd    1   3   0 wz--n-  55.90g  20.90g

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  mount
aufs on / type aufs (rw)
none on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
/dev/sdd1 on /cdrom type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=cp437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
/dev/loop0 on /rofs type squashfs (ro,noatime)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
/dev/sda1 on /mnt/slash type xfs (rw)
/dev/mapper/vgssd-var on /mnt/slash/var type ext4 (ro)
/dev/mapper/vgsata-usr on /mnt/usr type xfs (rw)
/dev/mapper/vgsata-var on /mnt/var type xfs (rw)
/dev/mapper/vgssd-usr on /mnt/slash/usr type ext4 (ro)

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  fdisk -l  

Disk /dev/sda: 1000.0 GB, 999989182464 bytes
255 heads, 63 sectors/track, 121575 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c3b74

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1         262     2104483+  83  Linux
/dev/sda2             263        2352    16787925   82  Linux swap / Solaris
/dev/sda3            2353      121575   957658747+  8e  Linux LVM

Disk /dev/sdb: 60.0 GB, 60022480896 bytes
32 heads, 32 sectors/track, 114483 cylinders
Units = cylinders of 1024 * 512 = 524288 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000cb60c

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1      114484    58615640   fd  Linux raid autodetect

Disk /dev/sdc: 60.0 GB, 60022480896 bytes
32 heads, 32 sectors/track, 114483 cylinders
Units = cylinders of 1024 * 512 = 524288 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000da964

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1      114484    58615640   fd  Linux raid autodetect

Disk /dev/sdd: 8011 MB, 8011120640 bytes
41 heads, 41 sectors/track, 9307 cylinders
Units = cylinders of 1681 * 512 = 860672 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000a7237

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1   *           5        9308     7819328    c  W95 FAT32 (LBA)

Disk /dev/md0: 60.0 GB, 60022325248 bytes
2 heads, 4 sectors/track, 14653888 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/md0 doesn't contain a valid partition table

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  pvs
  PV         VG     Fmt  Attr PSize   PFree  
  /dev/md0   vgssd  lvm2 a-    55.90g  20.90g
  /dev/sda3  vgsata lvm2 a-   913.29g 824.29g

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  uname -a
Linux usb-live 2.6.32-45-server #102-Ubuntu SMP Wed Jan 2 22:53:00 UTC 2013 x86_64 GNU/Linux

[08:07 06/13/13]
[root@usb-live /mnt/slash]
#  cat /proc/mdstat 
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
md0 : active raid1 sdc1[1] sdb1[0]
      58615552 blocks [2/2] [UU]
      
unused devices: <none>

[08:15 06/13/13]
[root@usb-live /mnt/slash]
#  fdisk -l

Disk /dev/sda: 1000.0 GB, 999989182464 bytes
255 heads, 63 sectors/track, 121575 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000c3b74

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1         262     2104483+  83  Linux
/dev/sda2             263        2352    16787925   82  Linux swap / Solaris
/dev/sda3            2353      121575   957658747+  8e  Linux LVM

Disk /dev/sdb: 60.0 GB, 60022480896 bytes
32 heads, 32 sectors/track, 114483 cylinders
Units = cylinders of 1024 * 512 = 524288 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000cb60c

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1      114484    58615640   fd  Linux raid autodetect

Disk /dev/sdc: 60.0 GB, 60022480896 bytes
32 heads, 32 sectors/track, 114483 cylinders
Units = cylinders of 1024 * 512 = 524288 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000da964

   Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1      114484    58615640   fd  Linux raid autodetect

Disk /dev/sdd: 8011 MB, 8011120640 bytes
41 heads, 41 sectors/track, 9307 cylinders
Units = cylinders of 1681 * 512 = 860672 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000a7237

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1   *           5        9308     7819328    c  W95 FAT32 (LBA)

Disk /dev/md0: 60.0 GB, 60022325248 bytes
2 heads, 4 sectors/track, 14653888 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/md0 doesn't contain a valid partition table

[08:15 06/13/13]
[root@usb-live /mnt/slash]
#  pvs
  PV         VG     Fmt  Attr PSize   PFree  
  /dev/md0   vgssd  lvm2 a-    55.90g  20.90g
  /dev/sda3  vgsata lvm2 a-   913.29g 824.29g

[08:17 06/13/13]
[root@usb-live /mnt/slash]
#  lvs
  LV        VG     Attr   LSize  Origin Snap%  Move Log Copy%  Convert
  home      vgsata -wi-a-  4.00g                                      
  mysql.bak vgsata -wi-a- 10.00g                                      
  sysbak    vgsata -wi-a- 50.00g                                      
  usr       vgsata -wi-ao  5.00g                                      
  var       vgsata -wi-ao 20.00g                                      
  mysqldump vgssd  -wi-a- 10.00g                                      
  usr       vgssd  -wi-ao  5.00g                                      
  var       vgssd  -wi-ao 20.00g                                      

[08:17 06/13/13]
[root@usb-live /mnt/slash]
#  cat /etc/lvm/
archive/  backup/   cache/    lvm.conf