I'm sure there are better ways of doing the 'split', but the following works for me:

use strict;
use warnings;
use diagnostics;

my %forchecking;
while (<DATA>) {
    chomp;
    my @sFields = split /\s+/;
    $forchecking{substr($sFields[3],0,5)} = $sFields[8];
}
__DATA__
Data Collected for SA120:Prct Dirty Cache Pages =            0
Data Collected for SA121:Prct Dirty Cache Pages =            1
Data Collected for SA122:Prct Dirty Cache Pages =            0
Data Collected for SA220:Prct Dirty Cache Pages =            0
Data Collected for SA221:Prct Dirty Cache Pages =            0
Data Collected for SA222:Prct Dirty Cache Pages =            17
[download]

Regards,

John Davies