my $rows = ...; # ref to AoH
my %ips;
foreach my $row (@$rows){
  $ips{ $row->{colIP} }->{ colPartitionSize } += $row->{colPartitionSize};
  $ips{ $row->{colIP} }->{ colPartitionFree } += $row->{colPartitionFree};
}
print Dumper \%ips;