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.

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'.   

 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   

Copy the partitions from one disk to the other:

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

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

Add the new disk to the raid array:

 [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   

Sanity check:

 [root@myServer ~]# cat /proc/mdstat  

 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! :)