Using xtrabackup for copying files can really saturate your disks, and that why we made special option
to limit rate of IO per second. But it really works when you do local copy.
What about stream backup ? Even you copy just to remote box with
innobackupex --stream=tar | ssh remotebox "tar xfi -"
, read may be so intensive so your mysqld feels impact, slave getting behind, etc…
For this there is a nice small utility – pv .
With pv you run:
innobackupex --stream=tar | pv -q -L10m | ssh remotebox "tar xfi -"
and it will limit channel rate to 10 M per second.