OK, but I am still struggling a little bit - what is the actual contents of @Colum_A?:

use Data::Dumper qw/Dumper/;

my $xls_path = "c:/path_to_xls.xlsx";
my $xls = $excel->Workbooks->Open("$xls_path");     

foreach my $sheet ( in $xls->Worksheets ) 
{
    $San ={};
    $San->{name} = $sheet->Name, $/;    
    
    my $San_data = $xls->Worksheets("$San->{name}");
    my @Colum_A = $San_data->UsedRange->{'Value'};

    ## what datastructure are we working with?
    print "SAN : $San->{name}\n";
    print Dumper \@Colum_A;
}
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If it is a long array like you say then why not take a simple approach?:

use strict;
use warnings;
use Data::Dumper qw/Dumper/;

#my $xls_path = "c:/path_to_xls.xlsx";
#my $xls = $excel->Workbooks->Open("$xls_path");
## just for testing
my $xls = [qw/san1 san2/];  
my $data;
#foreach my $sheet ( $xls->Worksheets ){
for my $sheet ( @$xls ){
    print "Data in SAN : $sheet\n";
    ## store each san as a hashref
    my $San ={};
    #$San->{name} = $sheet->Name, $/;
    $San->{name} = $sheet;
    
    #my $San_data = $xls->Worksheets("$San->{name}");
    #my @Colum_A = $San_data->UsedRange->{'Value'};
    
    ## again, just for testing
    my @Colum_A = qw/    RDUB010
                        34:34:36:7U
                        87:23:89:6C

                        RDUB090
                        90:39:12:6U
                        34:34:36:7Z
                        87:23:89:6N
                        34:38:36:7U
                    /;

    ## process each array element and print something appropriate
    ## also store data into a HoH / HoA
    my $current = 'not_defined'; # place holder
    foreach my $element (@Colum_A){
        if ($element =~ /^RD/){
              print "\tSAN : $San->{name}\n\t - LUN : $element\n";
              $current = $element;
        }
        elsif ( $element =~ /^(?:[^:]{2}:){3}[^:]{2}$/){
              # untested! should match
              # 60:05:08:b2:00:bb:b6:93
              print "\t\tWW : $element\n";
              push @{ $San->{LUN}->{$current} }, $element;
        }
        else {
            warn "Unrecognised input : \'$element\'\n";
        }
    }
    ## add San to data
    push @$data, $San;
}
## print out data structure
print "\n-----> DATA\n";
print Dumper $data;
## and again
print "\n-----> OUTPUT\n";
foreach my $san (@$data){
    print "SAN : $san->{name}\n";
    foreach my $lun( keys %{ $san->{LUN} } ){
        print " - LUN : $lun\n";
        print "\tWW : $_\n" for @{ $san->{LUN}->{$lun} }
    }
}
[download]

This produces what you seem to be looking for:

Data in SAN : san1
    SAN : san1
     - LUN : RDUB010
        WW : 34:34:36:7U
        WW : 87:23:89:6C
    SAN : san1
     - LUN : RDUB090
        WW : 90:39:12:6U
        WW : 34:34:36:7Z
        WW : 87:23:89:6N
        WW : 34:38:36:7U
Data in SAN : san2
    SAN : san2
     - LUN : RDUB010
        WW : 34:34:36:7U
        WW : 87:23:89:6C
    SAN : san2
     - LUN : RDUB090
        WW : 90:39:12:6U
        WW : 34:34:36:7Z
        WW : 87:23:89:6N
        WW : 34:38:36:7U

-----> DATA
$VAR1 = [
          {
            'LUN' => {
                       'RDUB090' => [
                                      '90:39:12:6U',
                                      '34:34:36:7Z',
                                      '87:23:89:6N',
                                      '34:38:36:7U'
                                    ],
                       'RDUB010' => [
                                      '34:34:36:7U',
                                      '87:23:89:6C'
                                    ]
                     },
            'name' => 'san1'
          },
          {
            'LUN' => {
                       'RDUB090' => [
                                      '90:39:12:6U',
                                      '34:34:36:7Z',
                                      '87:23:89:6N',
                                      '34:38:36:7U'
                                    ],
                       'RDUB010' => [
                                      '34:34:36:7U',
                                      '87:23:89:6C'
                                    ]
                     },
            'name' => 'san2'
          }
        ];

-----> OUTPUT
SAN : san1
 - LUN : RDUB090
    WW : 90:39:12:6U
    WW : 34:34:36:7Z
    WW : 87:23:89:6N
    WW : 34:38:36:7U
 - LUN : RDUB010
    WW : 34:34:36:7U
    WW : 87:23:89:6C
SAN : san2
 - LUN : RDUB090
    WW : 90:39:12:6U
    WW : 34:34:36:7Z
    WW : 87:23:89:6N
    WW : 34:38:36:7U
 - LUN : RDUB010
    WW : 34:34:36:7U
    WW : 87:23:89:6C
[download]

Update bugfixed code... Note to self - DO NOT POST UNTESTED REGEXES...