Tag: xen

Through our research and implementation of many Xen environments, it has become necessary to develop a reliable and secure method for backing up our Xen instances that are mounted on Logical Volumes (LVM).

The underlying problem is that the logical volume is usually a live file system that cannot be directly mounted / backed up or imaged safely.

We have written a script that processes all running Xen logical volumes, creates a snapshot of the volume and through that snapshot , uses dd to image the snapshot to another server over ssh.

You would be surprised at how well these dd images compress. Piping dd to bzip2 then to ssh to receive the image produces a very substantial compression ratio.

The initial trouble was writing the logic in the script to properly go through each Xen LV , create the snapshot, image and then remove the snapshot. Obviously extensive testing had to be completed to ensure reliability and proper error reporting.

This script should work with any 3rd party Xen control panel implementation (HyperVM, FluidVM, SolusVM to name a few). They all use the same underlying technology / framework. Since our script is a simple bash / shell script, it will run on any linux based system with little modification.

If you are using a LV for another purpose on the same box, it is probably a good idea to modify the script to ignore that so it doesn’t inadvertently get backed up.

Before implementing the script, it is probably a good idea to go through the motions manually just to see how it performs :

lvcreate -s -L 5G -n vm101_img_snapshot /dev/vps/vm101_img
dd if=/dev/vps/vm101_img_snapshot | bzip2 | ssh xenbackup@x.x.x.x "dd of=vm101_img.bz2"

One thing that you cant get around is space — you need to leave as much room as the largest Xen image on your logical volume — otherwise the script will fail at the snapshot creation process.

Find the script below. Hopefully it will help make your life easier (as well as being able to sleep at night) :

#!/bin/bash
# XEN Backup script
# Written by Star Dot Hosting

todaysdate=`date "+%Y-%m-%d"`

echo "XEN Backup Log: " $currentmonth > /var/log/backup.log
echo -e "------------------------------------" >> /var/log/backup.log
echo -e "" >> /var/log/backup.log


for obj0 in $(lvs --noheadings --separator ',' -o lv_name,lv_size | grep -v "swap" | awk -F "," '{printf "%sn", $1}');
do

#grab the snapshot size
snapsize=`lvs --noheadings --separator ',' -o lv_name,lv_size | grep -v "swap" | grep $obj0 | awk -F "," '{printf "%s", $2}'`

#create the snapshot
lvcreate -s -L $snapsize -n $obj0_snapshot /dev/xenlvm/$obj0 >> /var/log/backup.log 2>&1

#dd piped to bzip2 to compress the stream before piping it over the network via ssh to the destination box
dd if=/dev/xenlvm/$obj0_snapshot | bzip2 | ssh xenbackup@0.0.0.0 "dd of=/home/xenbackup/xen-backups/$obj0.$todaysdate.bz" >> /var/log/backup.log 2>&1

if [ "$?" -eq 1 ]
then
        echo -e "***SCRIPT FAILED, THERE WERE ERRORS***" >> /var/log/backup.log 2>&1
        cat /var/log/backup.log | mail -s "XEN Backup Job failed" admin@yourdomain.com
        lvremove -f /dev/xenlvm/$obj0_snapshot
        exit 1
else
        echo -e "Backup of $obj0 Completed Successfully!" >> /var/log/backup.log 2>&1
fi

# remove the snapshot
lvremove -f /dev/xenlvm/$obj0_snapshot


done

cat /var/log/backup.log | mail -s "XEN Backup Job Completed" admin@yourdomain.com

If you plan on automating this script in a cronjob, it may be a good idea to utilize ssh key authentication between your destination server and your Xen server.