====== Replace md mirror device ======


====== Background ======

System is Centos 5.6. \\
Warning in logwatch:- \\

  
  --------------------- Smartd Begin ------------------------ 
  
   
  Currently unreadable (pending) sectors detected:
  	/dev/sda - 96 Time(s)
  	53 unreadable sectors detected
   
  Offline uncorrectable sectors detected:
  	/dev/sda - 96 Time(s)
  	53 offline uncorrectable sectors detected
   
  ---------------------- Smartd End ------------------------- 


Boot device is /dev/sda, /dev/sdb did not have correct boot sector.


===== Fix non bootable /dev/sdb =====


Make /dev/sdb bootable:- \\


  [optimax]# grub
  
  GNU GRUB version 0.95 (640K lower / 3072K upper memory)
  
  [ Minimal BASH-like line editing is supported. For the first word, TAB
  lists possible command completions. Anywhere else TAB lists the possible
  completions of a device/filename.]
  
  grub> root (hd0,0)
  Filesystem type is ext2fs, partition type 0xfd
  
  grub> setup (hd0)
  Checking if "/boot/grub/stage1" exists... yes
  Checking if "/boot/grub/stage2" exists... yes
  Checking if "/boot/grub/e2fs_stage1_5" exists... yes
  Running "embed /boot/grub/e2fs_stage1_5 (hd0)"... 15 sectors are embedded.
  succeeded
  Running "install /boot/grub/stage1 (hd0) (hd0)1+15 p (hd0,0)/boot/grub/stage2
  /boot/grub/grub.conf"... succeeded
  Done.
  
  grub> root (hd1,0)
  Filesystem type is ext2fs, partition type 0xfd
  
  grub> setup (hd1)
  Checking if "/boot/grub/stage1" exists... yes
  Checking if "/boot/grub/stage2" exists... yes
  Checking if "/boot/grub/e2fs_stage1_5" exists... yes
  Running "embed /boot/grub/e2fs_stage1_5 (hd1)"... 15 sectors are embedded.
  succeeded
  Running "install /boot/grub/stage1 (hd1) (hd1)1+15 p (hd1,0)/boot/grub/stage2
  /boot/grub/grub.conf"... succeeded
  Done.
  
  grub> quit




===== Current md partitions =====


  [root@optiplex ~]# df -h
  Filesystem            Size  Used Avail Use% Mounted on
  /dev/md1               19G  4.1G   14G  23% /
  /dev/md3              303G  236G   53G  82% /data
  /dev/md2              1.9G  827M 1011M  45% /var
  /dev/md0               99M   37M   58M  39% /boot



===== Remove failed partitions from md arrays =====

Fail partitons:- \\

  # mdadm --manage /dev/md0 --fail /dev/sda1
  # mdadm --manage /dev/md1 --fail /dev/sda2
  
Remove from md arrays:-\\  
  
  # mdadm --manage /dev/md0 --remove /dev/sdb1
  # mdadm --manage /dev/md1 --remove /dev/sdb2
  
Shutdown system and replace faulty disk. If your disks are hot swap, this step may not be needed.\\
  
    # shutdown -h now

Swap over faulty disk for new disk.\\

Copy partiton table from existing good disk to new disk, double check you are copying the right partition table to the right disk. Then check again :-}

  # sfdisk -d /dev/sdb | sfdisk /dev/sda
  

Add partitons back in to md array:- \\

  # mdadm --manage /dev/md0 --add /dev/sda1
  mdadm: added /dev/sda1
  # mdadm --manage /dev/md1 --add /dev/sda2
  mdadm: added /dev/sda2


Watch the resync progress with:-\\

  # watch cat /proc/mdstat




Install grub loader back on to new disk.

  grub> find /grub/stage1
  (hd0,0)
  (hd1,0)
  
  grub> device (hd0) /dev/sdb (or /dev/hdb for IDE drives)
  grub> root (hd0,0)
  grub> setup (hd0)
  grub>quit