diff --git a/thin-provisioning/create_xml_data b/thin-provisioning/create_xml_data
index f6b442e..50b7bfd 100755
--- a/thin-provisioning/create_xml_data
+++ b/thin-provisioning/create_xml_data
@@ -40,8 +40,10 @@ end
 
 def check_opts(opts)
   abort "#{$prg} - 3 arguments required!" if opts.length < 3
+  abort "#{$prg} - block size must be > 0" if opts[:blocksize] <= 0
   abort "#{$prg} - size must be much greater/equal blocksize" if opts[:thinsize] < opts[:blocksize]
   abort "#{$prg} - number of thin provisioned devices or snapshots must be > 0" if opts[:thins].nil? || opts[:thins] == 0
+  abort "#{$prg} - size variation too large!" if !opts[:variation].nil? && (opts[:variation] > 2 * (opts[:thinsize] - opts[:blocksize]))
 end
 
 def parse_command_line(argv, units)
@@ -62,6 +64,9 @@ def parse_command_line(argv, units)
     o.on("-t", "--thins #THINS", Integer, "Sum of thin devices and snapshots.") do |mt|
       opts[:thins] = mt
     end
+    o.on("-v", "--size-variation SIZE[#{units[:chars]}]", String, "Size variation of thin devices and snapshots.") do |sv|
+      opts[:variation] = to_sectors(sv, units)
+    end
     o.on("-h", "--help", "Output this help.") do
       puts o
       exit
@@ -102,17 +107,26 @@ def range_mapping(from, to, length)
   "    <range_mapping time=\"0\" origin_begin=\"#{from}\" data_begin=\"#{to}\" length=\"#{length}\"/>\n"
 end
 
-def xml_metadata(opts, units)
-  blocks, to = opts[:thinsize] / opts[:blocksize], 0
+def blocks(opts)
+  opts[:thinsize] / opts[:blocksize]
+end
 
-  puts begin_superblock(opts[:blocksize], opts[:thins] * blocks)
-  0.step(opts[:thins] - 1) do |devid|
-    puts begin_device(devid, blocks)
+def this_blocks(opts)
+  opts[:variation].nil? ? blocks(opts) : (2 * opts[:thinsize] - rand(opts[:variation])) / 2 / opts[:blocksize]
+end
+
+def xml_metadata(opts, units)
+  to = 0
+
+  puts begin_superblock(opts[:blocksize], 2 * opts[:thins] * blocks(opts))
+  0.step(opts[:thins] - 1) do |dev_id|
+    b = this_blocks(opts)
+    puts begin_device(dev_id, b)
     if opts[:range]
-        puts range_mapping(0, to, blocks)
-        to += blocks
+      puts range_mapping(0, to, b)
+      to += b
     else
-      0.step(blocks - 1) do |from|
+      0.step(b - 1) do |from|
         puts single_mapping(from, to)
         to += 1
       end