You can compress the backups. Each file is
compressed independently. The compression reduces the
volume of the backup storage up to 90% according to file
type but the time necessary to the the first backup or
after a purge will be a little longer.
NOTE: The compression of a file that is already
compressed with a different format (jpg, video divx ,
zip folders ..) may not only not reduce the file size
but sometimes even get to a file slightly larger than
the original. So if your documents to backup are mainly
of this type, it is preferable not to use compression
and prefer an uncompressed faster backup.