This is script which backup KVM disk image by using ruby-libvirt

Test Enviroment

KVM on CentOS release 6.3 (Final)
ruby 1.9.3p194 (2012-04-20) [x86_64-linux]
ruby-libvirt (0.4.0)

Script

#
# KVM Disk Image Backup Script
#
#                fetaro@gmail.com
#
# usage : $ ruby kvmbackup.rb (domain-name)
#
# 1. Get Disk image paths from domain-xml
# 2. Susupend domain if running
# 3. Backup Disk image to BACKUP_DIR with BACKUP_CMD (cp or scp)
# 4. Resume domain if suspended
#
require 'libvirt'

BACKUP_CMD="scp"
#BACKUP_CMD="cp"
BACKUP_DIR="host:/path/to/backup/dir"
#BACKUP_DIR="/path/to/backup/dir"

if ARGV[0].nil?
  STDERR.puts "There is no argument"
  exit 1
end

domain=ARGV[0]
conn = Libvirt::open("qemu:///system")
dom = conn.lookup_domain_by_name(domain)

# get disk image path
img_paths = []
require "rexml/document"
xml = REXML::Document.new(dom.xml_desc)
xml.elements.to_a("domain/devices/disk").each do |disk|
  if disk.attributes["device"] == "disk"
    img_paths << disk.elements["source"].attributes["file"]
  end
end

return_code = 0
begin
  if dom.state[0] == 1 # domain is running
    puts "suspend #{domain}"
    dom.suspend
  end

  img_paths.each do |img_path|
    cmd = "#{BACKUP_CMD} #{img_path} #{BACKUP_DIR}"
    puts cmd
    system cmd
    if($? != 0) then
      STDERR.puts "fail to #{cmd}"
      return_code=1
    end
  end
rescue => e
  p e
  return_code = 1
ensure
  if dom.state[0] == 3 # domain is paused
    puts "resume #{domain}"
    dom.resume
  end
end

exit return_code