use warnings;
use strict;
use Data::Dumper;

my (%result, $subhash);

while (<DATA>) {
    if (/^Data_Value/ ... /^Data_raw/) {
        my @value = split;
        my $value = $value[0] = '';
        $value = "@value";


        if (/^Data_Value/) {
            $subhash = $value;
            $result{$subhash} = {};
        }

        $result{$subhash}->{Data_Group} = $value if /^Data_Group/;
        $result{$subhash}->{Data_raw} = $. if /^Data_raw/;
    }
}

print Dumper \%result;

__DATA__
Data_Value -999
Data_Group Clock453
Data_raw -from point_q/point2 \
         -of point_a/abc/Q/D \
         .
         .
         -to endpoint/abc/CK
Data_Value -123
Data_Group Clock453
Data_raw -from point_q/point2 \
         -of point_a/abc/Q/D \
         .
         .
         -to endpoint/abc/CK
Data_Value -666
Data_Group Clock453
Data_raw -from point_q/point2 \
         -of point_a/abc/Q/D \
         .
         .
         -to endpoint/abc/CK

##</code><code>##

user@unforgiven:~$ perl tst.pl
$VAR1 = {
          ' -123' => {
                       'Data_Group' => ' Clock453',
                       'Data_raw' => '10'
                     },
          ' -999' => {
                       'Data_Group' => ' Clock453',
                       'Data_raw' => '3'
                     },
          ' -666' => {
                       'Data_Group' => ' Clock453',
                       'Data_raw' => '17'
                     }
        };