Talk:Raid:Manual Rebuild

Please see my remarks at User_talk:Davidbray — Cactus (talk | contribs)  16:48, 19 March 2010 (UTC)

Thanks Cactus - I've made some changes here so look forward to your feedback

HowTo: Write the GRUB boot sector

Trex (talk) 00:26, 5 February 2013 (MST) Should add a note as per the comment 24 in this Bug re grub will not install on an unpartioned disk

Stephdl (talk) 12:24, 6 February 2013 (MST) ok i work on the howTo...work in progress, don't disturb :p

HowTo: Reinstate a disk from the RAID1 Array with the command Line

Look at the mdstat

First we must determine which drive is in default.

[root@ ~]#cat /proc/mdstat
Personalities : [raid1] 
md1 : active raid1 sdb1[1] sda1[0]
      104320 blocks [2/2] [UU]
      
md2 : active raid1 sdb2[2](F) sda2[0]
      52323584 blocks [2/1] [U_]
      
unused devices: <none>

(S)= Spare (F)= Fail [0]= number of the disk

	Note:
	As we can see the partition sdb2 is in default, we can see the flag: sdb2 [2] (F). We need to resynchronize the disk sdb to the existing array md2.

Fail and remove the disk, sdb in this case

[root@ ~]# mdadm --manage /dev/md2 --fail /dev/sdb2
mdadm: set /dev/sdb2 faulty in /dev/md2
[root@ ~]# mdadm --manage /dev/md2 --remove /dev/sdb2
mdadm: hot removed /dev/sdb2
[root@ ~]# mdadm --manage /dev/md1 --fail /dev/sdb1
mdadm: set /dev/sdb1 faulty in /dev/md1
[root@ ~]# mdadm --manage /dev/md1 --remove /dev/sdb1
mdadm: hot removed /dev/sdb1

Do your Disk Maintenance here

At this point the disk is idle.

[root@ ~]# cat /proc/mdstat
Personalities : [raid1] 
md1 : active raid1 sda1[0]
      104320 blocks [2/1] [U_]
      
md2 : active raid1 sda2[0]
      52323584 blocks [2/1] [U_]
      
unused devices: <none>

	Note:
	You'll have to determine if your disk can be reinstated at the array. In fact sometimes a raid can get out of sync after a power failure but also some times for physical outages of the hard disk. It is necessary to test the hard disk if this occurs repeatedly. For this we will use smartctl.

For all the details available by SMART on the disk

[root@ ~]# smartctl -a /dev/sdb

At least two types of tests are possible, short (~ 1 min) and long (~ 10 min to 90 min).

[root@ ~]# smartctl -t short /dev/sdb #short test
[root@ ~]# smartctl -t long  /dev/sdb #long test

to access the results / statistics for these tests:

[root@ ~]# smartctl -l selftest /dev/sdb

	Note:
	if you need to change the disk due to physical failure found by the smartctl command, install a new disk of the same capacity (or more) and enter the following commands to recreate new partitions by copying them from healthy disk sda.

[root@ ~]# sfdisk -d /dev/sda > sfdisk_sda.output
[root@ ~]# sfdisk /dev/sdb < sfdisk_sda.output

If you want to reinstate the same disk without replacing it, go to the next step.

Add the partitions back

[root@ ~]# mdadm --manage /dev/md1 --add /dev/sdb1
mdadm: hot added /dev/sdb1
[root@ ~]# mdadm --manage /dev/md2 --add /dev/sdb2
mdadm: hot added /dev/sdb2

Another Look at the mdstat

[root@sme8-64-dev ~]# cat /proc/mdstat
Personalities : [raid1] 
md1 : active raid1 sdb1[1] sda1[0]
      104320 blocks [2/2] [UU]
      
md2 : active raid1 sdb2[2] sda2[0]
      52323584 blocks [2/1] [U_]
      [>....................]  recovery =  1.9% (1041600/52323584) finish=14.7min speed=57866K/sec

unused devices: <none>

	Note:
	with a new disk it may be worthwhile to reinstall grub to avoid problems on startup error. The grub is the program that allows you to launch the operating systems.please enter the following commands.

HowTo: Write the GRUB boot sector

[root@ ~]# dd if=/dev/sda1 of=/dev/sdb1

[root@ ~]# 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> device (hd0) /dev/sdb

grub> root (hd0,0)
 Filesystem type is ext2fs, partition type 0xfd

grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... no
 Checking if "/grub/stage1" exists... yes
 Checking if "/grub/stage2" exists... yes
 Checking if "/grub/e2fs_stage1_5" exists... yes
 Running "embed /grub/e2fs_stage1_5 (hd0)"...  16 sectors are embedded.
succeeded
 Running "install /grub/stage1 (hd0) (hd0)1+16 p (hd0,0)/grub/stage2 /grub/grub.conf"... succeeded
Done.

grub> quit