let's explicitly use gzip level 5 here

see http://tukaani.org/lzma/benchmarks.html

lib/backup_restore/backuper.rb

@@ -258,7 +258,7 @@ module BackupRestore
       end
 
       log "Gzipping archive..."
-      `gzip #{tar_filename}`
+      `gzip -5 #{tar_filename}`
     end
 
     def after_create_hook