use strict;
use warnings;

my $data;
{
    local $/;
    $data = <DATA>;
}

my %drives = ();
while ($data =~ /^(\w+)\s*.*?Serial Number\.*(\w*)\s/smg) {
    $drives{$1} = $2;
}

while ( my ($key, $value) = each %drives) {
    print "$key  $value\n";
}

__DATA__
hdisk0   P1/Z1-Aa     16 Bit LVD SCSI Disk Drive (18200 MB)

        Manufacturer................IBM
        Machine Type and Model......ST318305LC
        FRU Number..................09P4437
        Serial Number...............0009E05B
        Part Number.................09P4436

hdisk1  P1/Z1-Ab     16 Bit LVD SCSI Disk Drive (18200 MB)

        Manufacturer................IBM
        Machine Type and Model......ST318305LC
        FRU Number..................09P4437
        Serial Number...............0004A0D2
        Part Number.................09P4436