How To Set Up Software RAID1 On A Running LVM System (Incl. GRUB2 Configuration) (Ubuntu 11.10) - Page 4

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  1. 8 Testing
  2. 9 Links

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:

[email protected]:~# 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>
[email protected]:~#

The output of

fdisk -l

should look as follows:

[email protected]:~# 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
[email protected]:~#

Now we copy the partition table of /dev/sda to /dev/sdb:

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

[email protected]:~# 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).)
[email protected]:~#

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

[email protected]:~# 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>
[email protected]:~#

Wait until the synchronization has finished:

[email protected]:~# 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>
[email protected]:~#

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.

 

Falko Timme

About Falko Timme

Falko Timme is an experienced Linux administrator and founder of Timme Hosting, a leading nginx business hosting company in Germany. He is one of the most active authors on HowtoForge since 2005 and one of the core developers of ISPConfig since 2000. He has also contributed to the O'Reilly book "Linux System Administration".

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