KVM: Backup VM disks without downtime
Note: I have been informed that there is a bug in Ubuntu related to snapshotted machines, which basically this scripts creates. Please read more here!!
UPDATE: There is an updated version of the script available here. It is based on the script below, but will have some additional features included.
As I have pondered using KVM as my hypervisor in the future, or aside my current setup, I was looking through the options when it came to backups. By default there are no “tools” to setup that will handle backups of the virtual machines. Though there seems to be some in the works. There are of course other solutions that have the functionality built in like Proxmox. A solution which I used earlier.
But the thought of having it working for a homemade solution where you have installed KVM on your machine was still itching. Therefore I wrote together the little script below which uses the following flow when triggered:
- Use virsh to get the disks from the VM specified.
- Use qemu-img to create a snapshot of the disk.
- Use qemu-img to convert the snapshot to an external file and move that file to the backup destination.
- Use qemu-img to delete the snapshot afterwards.
Note: The script does NOT make a complete backup of the VM, just a “clone” – if you will – of the disk(s) associated with the specified VM. The idea behind this is that it is quite fast, and easy, to just create a new Virtual Machine in KVM and specify the backed up image as hard drive in case a restore is needed.
The script can also be used to display disks for a VM, list possible snapshots (qemu), create snapshots (qemu) and backup multiple servers (see the -h flag in the script).
Here’s the script:
#!/bin/bash
#Script to backup KVM-machines using snapshots.
#Written by Jonas "Drakfot" Andersson
#Changelog
# Version 1.1
#20140309 – Initial scripting started.
#20140316 – Fixed an issue where a nonmounted drive (CD) could cause the script to fail.
#also sorted the part where the converted image will end up. Now the file is written
#directly to the destination instead of moved there after the conversion.
#Info:
#This script uses a combination of "virsh" and "qemu-img" to discover
#the disk images attached to a VM. When doing a backup a snapshot is
#done for each disk used by the VM and each snapshot is then exported
#as a .qcow2 file for backup.
#NOTE: This script do only backup the disk image file, not the entire
#VM. The idea behind this is that it is quick to create a new KVM-
#machine and specify the backup image as harddrive for the new machine.
### License ###
#KVM_Backup.sh – Quick script to backup KVM-machines without downtime.
#Copyright (C) 2014 Jonas Andersson
#This program is free software; you can redistribute it and/or modify
#it under the terms of the GNU General Public License as published by
#the Free Software Foundation; either version 3 of the License, or
#(at your option) any later version.
#
#This program is distributed in the hope that it will be useful,
#but WITHOUT ANY WARRANTY; without even the implied warranty of
#MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
#GNU General Public License for more details.
#
#You should have received a copy of the GNU General Public License
#along with this program; if not, write to the Free Software Foundation,
#Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
#Prerequisites
#KVM being used as VM hypervisor.
#qemu-img path specified in the variable below.
#virsh path specified in the variable below.
#Variables
BACKUPDIR=/backup
BACKUPNAME=backup_`date +%Y%m%d%HH%MM`
VIRSHBIN=/usr/bin/virsh
QEMUIMG=/usr/bin/qemu-img
VIRTUAL_DISKS=""
VMDOMAIN=""
#Functions!
function get_domain_disk () {
N=0
for i in `$VIRSHBIN domblklist $1 | tail -n+3 | sed -e ‘s/^-$//g’ | awk ‘{print $2}’` ; do
VIRTUAL_DISKS[$N]="$i"
let "N= $N + 1"
done
}
function create_snapshot () {
for disk in ${VIRTUAL_DISKS[*]}
do
echo "Creating snapshot for disk $disk"
$QEMUIMG snapshot -c $BACKUPNAME $disk
echo "Snapshot $BACKUPNAME created for disk $disk at `date`"
done
}
function convert_snapshot_qcow2 () {
for disk in ${VIRTUAL_DISKS[@]}
do
echo "Converting snapshot for disk $disk"
$QEMUIMG convert -f qcow2 -O qcow2 -s $BACKUPNAME $disk $BACKUPDIR/$VMDOMAIN.$BACKUPNAME.qcow2
#mv $disk.$BACKUPNAME.qcow2 $BACKUPDIR
echo "Snapshot for $disk converted at `date` and placed at $BACKUPDIR"
done
}
function delete_snapshot () {
for disk in ${VIRTUAL_DISKS[@]}
do
echo "Deleting snapshot $BACKUPNAME for disk $disk"
$QEMUIMG snapshot -d $BACKUPNAME $disk
echo "Snapshot $BACKUPNAME deleted at `date`"
done
}
function check_vmname () {
if [ -z $VMDOMAIN ]
then
echo "No VM specified, please input the name using $0 -n VMName <options>"
exit
fi
}
function list_disks () {
echo "$VMDOMAIN contains the following disk(s):"
for disk in ${VIRTUAL_DISKS[@]}
do
echo "$disk"
done
}
function list_snapshots () {
echo "Listing (possible) snapshots for $VMDOMAIN:"
for disk in ${VIRTUAL_DISKS[@]}
do
$QEMUIMG snapshot -l $disk
done
}
function multiple_servers () {
echo "File with multiple server names specified"
cat $SERVERLIST |while read line
do
VMDOMAIN=$line
echo "Backing up $VMDOMAIN"
get_domain_disk $VMDOMAIN
create_snapshot
convert_snapshot_qcow2
delete_snapshot
done
}
#Let’s check the args input and decide what functions to call based on them
while getopts ":n:blsc:d:hm:" opt; do
case "$opt" in
n)
if [ -a $OPTARG ]
then
SERVERLIST=$OPTARG
multiple_servers
exit
fi
VMDOMAIN=$OPTARG
;;
m)
BACKUPDIR=$OPTARG
echo "Backup destination set to $OPTARG"
;;
l)
check_vmname
get_domain_disk $VMDOMAIN
list_disks
;;
s)
get_domain_disk $VMDOMAIN
list_snapshots
;;
c)
get_domain_disk $VMDOMAIN
BACKUPNAME=$OPTARG
create_snapshot
;;
d)
get_domain_disk $VMDOMAIN
BACKUPNAME=$OPTARG
delete_snapshot
;;
echo "option -$OPTARG requires an argument."
;;
h)
echo "Usage: $0 -n VMname is required for useage."
echo "======================= Options available for $0: ======================="
echo "-b : Creates a snapshot of the disk, converts it to a qcow2 file and then moves it"
echo " to the backup destination, default is /backup."
echo " If a file with serverenames, one per row, is specified the script will loop"
echo " through the file and back up each server and its disk(s). No other options"
echo " will be parsed."
echo "-l : Lists the disks in the specified VM."
echo "-s : Lists the snapshots for the specified VM."
echo "-c : Creates snapshot(s) for the disk(s)in the specified VM. Requires an argument"
echo " to use as name for the snapshot. Eg -c snapshot_test"
echo "-d : Deletes the specified snapshot from the VM’s disk(s). Requires an argument"
echo " to use as name / ID specifying which snapshot to remove."
echo " Eg -d snapshot_test OR -d 1"
echo "-m : Specifies the destination where the backup will be saved. Default is /backup"
echo " NOTE: This option must be specified BEFORE the "-b" option to take effect!"
echo " Eg: -m /tmp/ -b"
;;
b)
echo "Backing up $VMDOMAIN"
get_domain_disk $VMDOMAIN
create_snapshot
convert_snapshot_qcow2
delete_snapshot
;;
?)
echo "Invalid option: -$OPTARG. Use $0 -h to display the syntax."
;;
esac
done
Some quick examples and their expected output
List the disk associated with a VM:
./kvm_backup.sh -n Test03 -l
Test03 contains the following disk(s):
/VMs/Test03.img
Create a snapshot of VM “Test03”:
./kvm_backup.sh -n Test03 -c test_snapshot
Creating snapshot for disk /VMs/Test03.img
Snapshot test_snapshot created for disk /VMs/Test03.img at Sun Mar 9 16:28:42 CET 2014
List snapshots for the VMs disk(s):
./kvm_backup.sh -n Test03 -s
Listing (possible) snapshots for Test03:
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
1 test_snapshot 0 2014-03-09 16:28:38 00:00:00.000
Delete a specific snapshot from VM (define either ID of TAG of the snapshot):
./kvm_backup.sh -n Test03 -d test_snapshot
Deleting snapshot test_snapshot for disk /VMs/Test03.img
Snapshot test_snapshot deleted at Sun Mar 9 16:28:56 CET 2014
If your VM has multiple disks, the listing will look like this:
./kvm_backup.sh -n Test04 -l
Test04 contains the following disk(s):
/VMs/Test04.img
/VMs/Test04-disk02.img