Back Up (And Restore) LVM Partitions With LVM Snapshots - Page 2
Back Up (And Restore) LVM Partitions With LVM Snapshots - Page 3
Back Up (And Restore) LVM Partitions With LVM Snapshots
Version 1.1
Author: Falko Timme
Last edited 04/18/2007
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 restore the / partition from your backup (covered in the last chapter of this tutorial) you need a Linux Live-CD that supports LVM, such as Knoppix or the Debian Etch Netinstall CD which you can use as a rescue CD if you specify rescue at the boot prompt. I will use the Debian Etch Netinstall CD in this example (the list of mirrors is available here: http://www.debian.org/CD/http-ftp/ - I downloaded this one: http://ftp.de.debian.org/debian-cd/4.0_r0/i386/iso-cd/debian-40r0-i386-netinst.iso).
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.
To learn more about LVM, you should read this tutorial: http://www.howtoforge.com/linux_lvm
2 Create The /backups LVM Partition
(If you'd like to store your backups somewhere else, e.g on an external USB drive, you don't have to do this.)
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 -lDisk /dev/sda: 10.7 GB, 10737418240 bytes255 heads, 63 sectors/track, 1305 cylindersUnits = 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 LVMDisk /dev/sdb: 64.4 GB, 64424509440 bytes255 heads, 63 sectors/track, 7832 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytesDisk /dev/sdb doesn't contain a valid partition tableDisk /dev/dm-0: 9990 MB, 9990832128 bytes255 heads, 63 sectors/track, 1214 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytesDisk /dev/dm-0 doesn't contain a valid partition tableDisk /dev/dm-1: 486 MB, 486539264 bytes255 heads, 63 sectors/track, 59 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytesDisk /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 /boot partition (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/sdbDevice contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabelBuilding a new DOS disklabel. Changes will remain in memory only,until you decide to write them. After that, of course, the previouscontent 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): <-- nCommand action e extended p primary partition (1-4)<-- pPartition number (1-4): <-- 1First cylinder (1-7832, default 1): <-- [ENTER] Using default value 1Last cylinder or +size or +sizeM or +sizeK (1-7832, default 7832): <-- [ENTER] Using default value 7832Command (m for help): <-- tSelected partition 1Hex code (type L to list codes): <-- 8eChanged system type of partition 1 to 8e (Linux LVM)Command (m for help): <-- wThe partition table has been altered!Calling ioctl() to re-read partition table.Syncing disks.
pvcreate /dev/sdb1vgextend server1 /dev/sdb1lvcreate --name backups --size 30G server1mkfs.ext3 /dev/mapper/server1-backupsmkdir /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
