How To Set Up Software RAID1 On A Running LVM System (Incl. GRUB2 Configuration) (Ubuntu 11.10) - Page 4
8 Testing
Now let's simulate a hard drive failure. It doesn't matter if you select /dev/sda or /dev/sdb here. In this example I assume that /dev/sdb has failed.
To simulate the hard drive failure, you can either shut down the system and remove /dev/sdb from the system, or you (soft-)remove it like this:
mdadm --manage /dev/md0 --fail /dev/sdb1
mdadm --manage /dev/md1 --fail /dev/sdb5
mdadm --manage /dev/md0 --remove /dev/sdb1
mdadm --manage /dev/md1 --remove /dev/sdb5
Shut down the system:
shutdown -h now
Then put in a new /dev/sdb drive (if you simulate a failure of /dev/sda, you should now put /dev/sdb in /dev/sda's place and connect the new HDD as /dev/sdb!) and boot the system. It should still start without problems.
Now run
cat /proc/mdstat
and you should see that we have a degraded array:
root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sda1[2]
248820 blocks super 1.2 [2/1] [U_]
md1 : active raid1 sda5[2]
4989940 blocks super 1.2 [2/1] [U_]
unused devices: <none>
root@server1:~#
The output of
fdisk -l
should look as follows:
root@server1:~# fdisk -l
Disk /dev/sda: 5368 MB, 5368709120 bytes
255 heads, 63 sectors/track, 652 cylinders, total 10485760 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0000ad1b
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 499711 248832 fd Linux raid autodetect
/dev/sda2 501758 10483711 4990977 5 Extended
/dev/sda5 501760 10483711 4990976 fd Linux raid autodetect
Disk /dev/sdb: 5368 MB, 5368709120 bytes
255 heads, 63 sectors/track, 652 cylinders, total 10485760 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/sdb doesn't contain a valid partition table
Disk /dev/md1: 5109 MB, 5109698560 bytes
2 heads, 4 sectors/track, 1247485 cylinders, total 9979880 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/md1 doesn't contain a valid partition table
Disk /dev/md0: 254 MB, 254791680 bytes
2 heads, 4 sectors/track, 62205 cylinders, total 497640 sectors
Units = sectors of 1 * 512 = 512 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
Disk /dev/mapper/server1-root: 4563 MB, 4563402752 bytes
255 heads, 63 sectors/track, 554 cylinders, total 8912896 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/server1-root doesn't contain a valid partition table
Disk /dev/mapper/server1-swap_1: 532 MB, 532676608 bytes
255 heads, 63 sectors/track, 64 cylinders, total 1040384 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/server1-swap_1 doesn't contain a valid partition table
root@server1:~#
Now we copy the partition table of /dev/sda to /dev/sdb:
sfdisk -d /dev/sda | sfdisk --force /dev/sdb
root@server1:~# sfdisk -d /dev/sda | sfdisk --force /dev/sdb
Warning: extended partition does not start at a cylinder boundary.
DOS and Linux will interpret the contents differently.
Checking that no-one is using this disk right now ...
OK
Disk /dev/sdb: 652 cylinders, 255 heads, 63 sectors/track
sfdisk: ERROR: sector 0 does not have an msdos signature
/dev/sdb: unrecognized partition table type
Old situation:
No partitions found
New situation:
Units = sectors of 512 bytes, counting from 0
Device Boot Start End #sectors Id System
/dev/sdb1 * 2048 499711 497664 fd Linux raid autodetect
/dev/sdb2 501758 10483711 9981954 5 Extended
/dev/sdb3 0 - 0 0 Empty
/dev/sdb4 0 - 0 0 Empty
/dev/sdb5 501760 10483711 9981952 fd Linux raid autodetect
Warning: partition 1 does not end at a cylinder boundary
Successfully wrote the new partition table
Re-reading the partition table ...
If you created or changed a DOS partition, /dev/foo7, say, then use dd(1)
to zero the first 512 bytes: dd if=/dev/zero of=/dev/foo7 bs=512 count=1
(See fdisk(8).)
root@server1:~#
Afterwards we remove any remains of a previous RAID array from /dev/sdb...
mdadm --zero-superblock /dev/sdb1
mdadm --zero-superblock /dev/sdb5
... and add /dev/sdb to the RAID array:
mdadm -a /dev/md0 /dev/sdb1
mdadm -a /dev/md1 /dev/sdb5
Now take a look at
cat /proc/mdstat
root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb1[3] sda1[2]
248820 blocks super 1.2 [2/2] [UU]
md1 : active raid1 sdb5[3] sda5[2]
4989940 blocks super 1.2 [2/1] [U_]
[===>.................] recovery = 15.6% (779648/4989940) finish=4.7min speed=14609K/sec
unused devices: <none>
root@server1:~#
Wait until the synchronization has finished:
root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb1[3] sda1[2]
248820 blocks super 1.2 [2/2] [UU]
md1 : active raid1 sdb5[3] sda5[2]
4989940 blocks super 1.2 [2/2] [UU]
unused devices: <none>
root@server1:~#
Then install the bootloader on both HDDs:
grub-install /dev/sda
grub-install /dev/sdb
That's it. You've just replaced a failed hard drive in your RAID1 array.
9 Links
- The Software-RAID Howto: http://tldp.org/HOWTO/Software-RAID-HOWTO.html
- Ubuntu: http://www.ubuntu.com/
