This tutorial shows how you can create backups of LVM partitions with an LVM feature called LVM snapshots. An LVM snapshot is an exact copy of an LVM partition that has all the data from the LVM volume from the time the snapshot was created. The big advantage of LVM snapshots is that they can be used to greatly reduce the amount of time that your services/databases are down during backups because a snapshot is usually created in fractions of a second. After the snapshot has been created, you can back up the snapshot while your services and databases are in normal operation.
I will also show how to restore an LVM partition from a backup in an extra chapter at the end of this tutorial.
This document comes without warranty of any kind! I do not issue any guarantee that this will work for you!
1 Preliminary Note
I have tested this on a Debian Etch server with the IP address 192.168.0.100 and the hostname server1.example.com. It has two hard disks:
- /dev/sda (10GB) that contains a small /boot partition (non-LVM), a / partition (LVM, a little less than 10GB), and a swap partition (LVM)
- /dev/sdb (60GB), unused at the moment; will be used to create a 30GB /backups partition (LVM) and for the snapshots of the / partition (10GB - that's enough because the / partition is a little less than 10GB).
I have created a
Debian Etch VMware image that you can download and run in VMware Server or VMware Player (see
http://www.howtoforge.com/import_vmware_images to learn how to do that). It has the same specifications as my test system from above. The root password is
howtoforge. Using that VMware image, you can do the exact same steps than me in this tutorial to get used to using LVM snapshots.
To create a backup of the / partition I will proceed as follows: I will create a snapshot of the / partition, and afterwards I will create a backup of the snapshot (instead of the actual / partition!) on the /backups partition (of course, you can store that backup wherever you want - instead of creating an extra /backups LVM partition, you could also use an external USB drive). The backup can be made using your preferred backup solution, e.g. with tar or dd. Afterwards, I'll destroy the snapshot because it isn't needed anymore and would use system resources.
You don't necessarily need a second HDD for the snapshots - you can use the first one provided you have enough free (unpartitioned) space left on it to create snapshots on it (you should use the same space for the snapshots that you use for the partition that you want to back up). And as mentioned before, you can use a USB drive for backing up the snapshots.
2 Create The /backups LVM Partition
Our current situation is as follows:
pvdisplay
server1:~# pvdisplay
--- Physical volume ---
PV Name /dev/sda5
VG Name server1
PV Size 9.76 GB / not usable 0
Allocatable yes (but full)
PE Size (KByte) 4096
Total PE 2498
Free PE 0
Allocated PE 2498
PV UUID vQIUga-221O-GIKj-81Ct-2ITT-bKPw-kKElpM
vgdisplay
server1:~# vgdisplay
--- Volume group ---
VG Name server1
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 2
Max PV 0
Cur PV 1
Act PV 1
VG Size 9.76 GB
PE Size 4.00 MB
Total PE 2498
Alloc PE / Size 2498 / 9.76 GB
Free PE / Size 0 / 0
VG UUID jkWyez-c0nT-LCaE-Bzvi-Q4oD-eD3Q-BKIOFC
lvdisplay
server1:~# lvdisplay
--- Logical volume ---
LV Name /dev/server1/root
VG Name server1
LV UUID UK1rjH-LS3l-f7aO-240S-EwGw-0Uws-5ldhlW
LV Write Access read/write
LV Status available
# open 1
LV Size 9.30 GB
Current LE 2382
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:0
--- Logical volume ---
LV Name /dev/server1/swap_1
VG Name server1
LV UUID 2PASi6-fQV4-I8sJ-J0yq-Y9lH-SJ32-F9jHaj
LV Write Access read/write
LV Status available
# open 2
LV Size 464.00 MB
Current LE 116
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:1
fdisk -l
server1:~# fdisk -l
Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 31 248976 83 Linux
/dev/sda2 32 1305 10233405 5 Extended
/dev/sda5 32 1305 10233373+ 8e Linux LVM
Disk /dev/sdb: 64.4 GB, 64424509440 bytes
255 heads, 63 sectors/track, 7832 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk /dev/sdb doesn't contain a valid partition table
Disk /dev/dm-0: 9990 MB, 9990832128 bytes
255 heads, 63 sectors/track, 1214 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk /dev/dm-0 doesn't contain a valid partition table
Disk /dev/dm-1: 486 MB, 486539264 bytes
255 heads, 63 sectors/track, 59 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk /dev/dm-1 doesn't contain a valid partition table
So /dev/sda contains the logical volumes /dev/server1/root (/ partition) and /dev/server1/swap_1 (swap partition) plus a small /bootpartition (non-LVM).
(BTW, /dev/server1/root is the same as /dev/mapper/server1-root on Debian Etch. The first is a symlink to the second; I will use both notations in this tutorial. The same goes for /dev/server1/swap_1 and /dev/mapper/server1-swap_1.)
I will now create the partition /dev/sdb1 and add it to the server1 volume group, and afterwards I will create the volume/dev/server1/backups (which will be 30GB instead of the full 60GB of /dev/sdb so that we have enough space left for the snapshots) which I will mount on /backups:
fdisk /dev/sdb
server1:~# fdisk /dev/sdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.
The number of cylinders for this disk is set to 7832.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help): <-- n
Command action
e extended
p primary partition (1-4)
<-- p
Partition number (1-4): <-- 1
First cylinder (1-7832, default 1): <-- [ENTER]
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-7832, default 7832): <-- [ENTER]
Using default value 7832
Command (m for help): <-- t
Selected partition 1
Hex code (type L to list codes): <-- 8e
Changed system type of partition 1 to 8e (Linux LVM)
Command (m for help): <-- w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
pvcreate /dev/sdb1
vgextend server1 /dev/sdb1
lvcreate --name backups --size 30G server1
mkfs.ext3 /dev/mapper/server1-backups
mkdir /backups
Now let's mount our /dev/server1/backups volume on /backups:
mount /dev/mapper/server1-backups /backups
To have that volume mounted automatically whenever you boot the system, you must edit /etc/fstab and add a line like this to it:
vi /etc/fstab
[...]
/dev/mapper/server1-backups /backups ext3 defaults,errors=remount-ro 0 1 |
Now our new situation looks like this:
pvdisplay
server1:~# pvdisplay
--- Physical volume ---
PV Name /dev/sda5
VG Name server1
PV Size 9.76 GB / not usable 0
Allocatable yes (but full)
PE Size (KByte) 4096
Total PE 2498
Free PE 0
Allocated PE 2498
PV UUID vQIUga-221O-GIKj-81Ct-2ITT-bKPw-kKElpM
--- Physical volume ---
PV Name /dev/sdb1
VG Name server1
PV Size 59.99 GB / not usable 0
Allocatable yes
PE Size (KByte) 4096
Total PE 15358
Free PE 7678
Allocated PE 7680
PV UUID cvl1H5-cxRe-iyNg-m2mM-tjxM-AvER-rjqycO
vgdisplay
server1:~# vgdisplay
--- Volume group ---
VG Name server1
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 5
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 3
Open LV 3
Max PV 0
Cur PV 2
Act PV 2
VG Size 69.75 GB
PE Size 4.00 MB
Total PE 17856
Alloc PE / Size 10178 / 39.76 GB
Free PE / Size 7678 / 29.99 GB
VG UUID jkWyez-c0nT-LCaE-Bzvi-Q4oD-eD3Q-BKIOFC
lvdisplay
server1:~# lvdisplay
--- Logical volume ---
LV Name /dev/server1/root
VG Name server1
LV UUID UK1rjH-LS3l-f7aO-240S-EwGw-0Uws-5ldhlW
LV Write Access read/write
LV Status available
# open 1
LV Size 9.30 GB
Current LE 2382
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:0
--- Logical volume ---
LV Name /dev/server1/swap_1
VG Name server1
LV UUID 2PASi6-fQV4-I8sJ-J0yq-Y9lH-SJ32-F9jHaj
LV Write Access read/write
LV Status available
# open 2
LV Size 464.00 MB
Current LE 116
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:1
--- Logical volume ---
LV Name /dev/server1/backups
VG Name server1
LV UUID sXq2Xe-y2CE-Ycko-rCoE-M5kl-E1vH-KQRoP6
LV Write Access read/write
LV Status available
# open 1
LV Size 30.00 GB
Current LE 7680
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:2
3 Create An LVM Snapshot Of /
Now it's time to create the snapshot of the /dev/server1/root volume. We will call the snapshot rootsnapshot:
lvcreate -L10G -s -n rootsnapshot /dev/server1/root
The output of
lvdisplay
should look like this:
server1:~# lvdisplay
--- Logical volume ---
LV Name /dev/server1/root
VG Name server1
LV UUID UK1rjH-LS3l-f7aO-240S-EwGw-0Uws-5ldhlW
LV Write Access read/write
LV snapshot status source of
/dev/server1/rootsnapshot [active]
LV Status available
# open 1
LV Size 9.30 GB
Current LE 2382
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:0
--- Logical volume ---
LV Name /dev/server1/swap_1
VG Name server1
LV UUID 2PASi6-fQV4-I8sJ-J0yq-Y9lH-SJ32-F9jHaj
LV Write Access read/write
LV Status available
# open 2
LV Size 464.00 MB
Current LE 116
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:1
--- Logical volume ---
LV Name /dev/server1/backups
VG Name server1
LV UUID sXq2Xe-y2CE-Ycko-rCoE-M5kl-E1vH-KQRoP6
LV Write Access read/write
LV Status available
# open 1
LV Size 30.00 GB
Current LE 7680
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:2
--- Logical volume ---
LV Name /dev/server1/rootsnapshot
VG Name server1
LV UUID 9zR5X5-OhM5-xUI0-OolP-vLjG-pexO-nk36oz
LV Write Access read/write
LV snapshot status active destination for /dev/server1/root
LV Status available
# open 1
LV Size 9.30 GB
Current LE 2382
COW-table size 10.00 GB
COW-table LE 2560
Allocated to snapshot 0.01%
Snapshot chunk size 8.00 KB
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 254:5
We want to mount /dev/server1/rootsnapshot on /mnt/server1/rootsnapshot, so we have to create that directory first:
mkdir -p /mnt/server1/rootsnapshot
Then we mount our snapshot:
mount /dev/server1/rootsnapshot /mnt/server1/rootsnapshot
Then we run
ls -l /mnt/server1/rootsnapshot/
This should show all directories and files that we know from our / partition:
server1:~# ls -l /mnt/server1/rootsnapshot/
total 132
drwxr-xr-x 2 root root 4096 2007-04-10 21:02 backups
drwxr-xr-x 2 root root 4096 2007-04-10 20:35 bin
drwxr-xr-x 2 root root 4096 2007-04-10 20:25 boot
lrwxrwxrwx 1 root root 11 2007-04-10 20:25 cdrom -> media/cdrom
drwxr-xr-x 13 root root 40960 2007-04-10 20:36 dev
drwxr-xr-x 57 root root 4096 2007-04-10 21:09 etc
drwxr-xr-x 3 root root 4096 2007-04-10 20:36 home
drwxr-xr-x 2 root root 4096 2007-04-10 20:26 initrd
lrwxrwxrwx 1 root root 28 2007-04-10 20:29 initrd.img -> boot/initrd.img-2.6.18-4-486
drwxr-xr-x 13 root root 4096 2007-04-10 20:34 lib
drwx------ 2 root root 16384 2007-04-10 20:25 lost+found
drwxr-xr-x 4 root root 4096 2007-04-10 20:25 media
drwxr-xr-x 2 root root 4096 2006-10-28 16:06 mnt
drwxr-xr-x 2 root root 4096 2007-04-10 20:26 opt
drwxr-xr-x 2 root root 4096 2006-10-28 16:06 proc
drwxr-xr-x 3 root root 4096 2007-04-10 20:42 root
drwxr-xr-x 2 root root 4096 2007-04-10 20:36 sbin
drwxr-xr-x 2 root root 4096 2007-03-07 23:56 selinux
drwxr-xr-x 2 root root 4096 2007-04-10 20:26 srv
drwxr-xr-x 2 root root 4096 2007-01-30 23:27 sys
drwxrwxrwt 2 root root 4096 2007-04-10 21:09 tmp
drwxr-xr-x 10 root root 4096 2007-04-10 20:26 usr
drwxr-xr-x 13 root root 4096 2007-04-10 20:26 var
lrwxrwxrwx 1 root root 25 2007-04-10 20:29 vmlinuz -> boot/vmlinuz-2.6.18-4-486
So our snapshot has successfullly been created!
Now we can create a backup of the snapshot on the /backups partition using our preferred backup solution. For example, if you like to do a file-based backup, you can do it like this:
tar -pczf /backups/root.tar.gz /mnt/server1/rootsnapshot
And if you like to do a bitwise backup (i.e. an image), you can do it like this:
dd if=/dev/server1/rootsnapshot of=/backups/root.dd
server1:~# dd if=/dev/server1/rootsnapshot of=/backups/root.dd
19513344+0 records in
19513344+0 records out
9990832128 bytes (10 GB) copied, 320.059 seconds, 31.2 MB/s
You could also use both ways to be prepared for whatever might happen to your /dev/server1/root volume. In this case, you should have two backups afterwards:
ls -l /backups/
server1:~# ls -l /backups/
total 9947076
drwx------ 2 root root 16384 2007-04-10 21:04 lost+found
-rw-r--r-- 1 root root 9990832128 2007-04-10 21:28 root.dd
-rw-r--r-- 1 root root 184994590 2007-04-10 21:18 root.tar.gz
Afterwards, we unmount and remove the snapshot to prevent it from consuming system resources:
umount /mnt/server1/rootsnapshot
lvremove /dev/server1/rootsnapshot
That's it, you've just made your first backup from an LVM snapshot.
4 Restore A Backup
This chapter is about restoring the /dev/server1/root volume from the dd image we've created in the previous chapter. Normally you can restore a backup from the same running system if the volume that you want to restore doesn't contain system-critical files. But because the/dev/server1/root volume is the system partition of our machine, we must use a rescue system or Live-CD to restore the backup. The rescue system/Live-CD must support LVM.
To restore the /dev/server1/root volume, I boot the system from the Debian Etch Netinstall CD and type in rescue at the boot prompt:
Select your language:
Choose your country:
Choose your keyboard layout:
You can accept the default hostname:
You can also accept the default domain name (which is empty):
Select the backup volume (/dev/server1/backups) as the root file system:
Then select Execute a shell in the installer environment:
Hit Continue:
Now we have a shell:
Run
mount
and you should see that /dev/server1/backups is mounted on /target. So the dd image of the /dev/server1/root volume should be/target/root.dd. To restore it, we simply run
dd if=/target/root.dd of=/dev/server1/root
That's it. It can take a few minutes until the task is finished. Afterwards you can remove the Live-CD and boot into the normal system again.
