Here is what I use (UNIX):

#!/usr/bin/bash
TOTAL=0
printf "\ntotal size of FULL backups for the last week run, by the 
groups:\n"
for ,list all your active groups here> 
do
  SIZE=`mminfo -ar totalsize -t'last week' -qlevel=full,group=$NSRgroup | 
awk '{sum=sum+$0};END {print sum}'`   
  SIZEgb=`expr $SIZE / 1073741824`
  TOTAL=`expr $TOTAL + $SIZEgb`
  printf $NSRgroup":\t"$SIZEgb" GB\n"
done
printf "====\nTOTAL:\t\t$TOTAL GB\n\n"
[/code]

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