by Ken Task.
Backup and restore processes are memory hogs! To see just how much, run a backup process of one of the largest courses while, at the same time, having a terminal window opened logged on as root using 'top'.
Spikes to 100% of CPU not unusual. :|
Suggestion: run mysqltuner
https://raw.github.com/major/MySQLTuner-perl/master/mysqltuner.pl
and see what suggestions for tweaking it has.
'spirit of sharing', Ken