How to Replace a Failed Disk

Steps to fix a hard drive failure that is in a raid 1 configuration:

The following demonstrates what a failed disk looks like:

[root@myServer ~]# cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdb1[0] sda1[2](F)
128384 blocks [2/1] [U_]
md1 : active raid1 sdb2[0] sda2[2](F)
16779776 blocks [2/1] [U_]
md2 : active raid1 sdb3[0] sda3[2](F)
139379840 blocks [2/1] [U_]
unused devices: <none>

[root@myServer ~]# smartctl -a /dev/sda
smartctl 5.42 2011-10-20 r3458 [x86_64-linux-2.6.18-371.1.2.el5] (local build)
Copyright (C) 2002-11 by Bruce Allen, http://smartmontools.sourceforge.net

Short INQUIRY response, skip product id
A mandatory SMART command failed: exiting. To continue, add one or more '-T permissive' options.

[root@myServer ~]# smartctl -a /dev/sdb
smartctl 5.42 2011-10-20 r3458 [x86_64-linux-2.6.18-371.1.2.el5] (local build)
Copyright (C) 2002-11 by Bruce Allen, http://smartmontools.sourceforge.net

=== START OF INFORMATION SECTION ===
Model Family: Seagate Barracuda 7200.10
Device Model: ST3160815AS
Serial Number: 9RA6DZP8
Firmware Version: 4.AAB
User Capacity: 160,041,885,696 bytes [160 GB]
Sector Size: 512 bytes logical/physical
Device is: In smartctl database [for details use: -P show]
ATA Version is: 7
ATA Standard is: Exact ATA specification draft version not indicated
Local Time is: Mon Sep 8 15:50:48 2014 PDT
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

There is a lot more that gets printed, but I cut it out.

So /dev/sda has clearly failed.

Here are the steps:

Take note of the GOOD disk serial number so I leave that one in when I replace it:
Serial Number: 9RA6DZP8

Mark and remove failed disk from raid:

[root@myServer ~]# mdadm --manage /dev/md0 --fail /dev/sda1
mdadm: set /dev/sda1 faulty in /dev/md0

[root@myServer ~]# mdadm --manage /dev/md1 --fail /dev/sda2
mdadm: set /dev/sda2 faulty in /dev/md1

[root@myServer ~]# mdadm --manage /dev/md2 --fail /dev/sda3
mdadm: set /dev/sda3 faulty in /dev/md2

[root@myServer ~]# mdadm --manage /dev/md0 --remove /dev/sda1
mdadm: hot removed /dev/sda1

[root@myServer ~]# mdadm --manage /dev/md1 --remove /dev/sda2
mdadm: hot removed /dev/sda2

[root@myServer ~]# mdadm --manage /dev/md2 --remove /dev/sda3
mdadm: hot removed /dev/sda3

Make sure grub is installed on the good disk and that grub.conf is updated:

[root@myServer ~]# grub-install /dev/sdb
Installation finished. No error reported.
This is the contents of the device map /boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.

1. this device map was generated by anaconda
   

(hd0) /dev/sda
(hd1) /dev/sdb

Take note of the which hd partition corresponds with the good disk, ie hd1 in this case.

[root@myServer ~]# vim /boot/grub/menu.lst

Add fallback=1 right after default=0
Go to the bottom section where you should find some kernel stanzas.
Copy the first of them and paste the stanza before the first existing stanza; replace root (hd0,0) with root (hd1,0)
Should look like this:

[...]
title CentOS (2.6.18-128.el5)
root (hd1,0)
kernel /vmlinuz-2.6.18-128.el5 ro root=/dev/VolGroup00/LogVol00
initrd /initrd-2.6.18-128.el5.img
title CentOS (2.6.18-128.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-128.el5 ro root=/dev/
initrd /initrd-2.6.18-128.el5.img

Save and quit

[root@myServer ~]# mv /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.bak

[root@myServer ~]# mkinitrd /boot/initramfs-$(uname -r).img $(uname -r)

[root@myServer ~]# init 0

Swap the bad drive with the new drive and boot the machine.

Once it's booted:

Check the device names with cat /proc/mdstat and/or fisk -l.
The newly installed drive on myServer was named /dev/sda.

[root@myServer ~]# modeprobe raid1

[root@myServer ~]# modeprobe linear

[root@myServer ~]# sfdisk -d /dev/sdb | sfdisk --force /dev/sda

[root@myServer ~]# sfdisk -l => sanity check

[root@myServer ~]# mdadm --manage /dev/md0 --add /dev/sda1
mdadm: added /dev/sda1

[root@myServer ~]# mdadm --manage /dev/md1 --add /dev/sda2
mdadm: added /dev/sda2

[root@myServer ~]# mdadm --manage /dev/md2 --add /dev/sda3
mdadm: added /dev/sda3

[root@myServer ~]# cat /proc/mdstat => Sanity check
Personalities : [raid1] [linear]
md0 : active raid1 sda1[1] sdb1[0]
128384 blocks [2/2] [UU]

md1 : active raid1 sda2[2] sdb2[0]
16779776 blocks [2/1] [U_]
[>....................] recovery = 3.2% (548864/16779776) finish=8.8min speed=30492K/sec

md2 : active raid1 sda3[2] sdb3[0]
139379840 blocks [2/1] [U_]
resync=DELAYED

unused devices: <none>

That's it! :)