I like the following way:

use strict;
use warnings;
use Data::Dumper;
my @data;
while( <DATA> ) {
    chop;
    if ( /^(array.*|unassigned)$/ ) {
        push @data, $1;
    } else {
        $data[-1] .= " $_";
    }
}
print Dumper \@data;
__DATA__
array A
physicaldrive 2C:1:1 port 2C:box 1:bay 1 SAS 1 TB OK
physicaldrive 2C:1:2 port 2C:box 1:bay 2 SAS 1 TB OK
array B
physicaldrive 2C:1:3 port 2C:box 1:bay 3 SAS 1 TB OK
physicaldrive 2C:1:4 port 2C:box 1:bay 4 SAS 1 TB OK
unassigned
physicaldrive 7C:3:7 port 7C:box 3:bay 7 SAS 1 TB OK
physicaldrive 7C:3:8 port 7C:box 3:bay 8 SAS 1 TB OK
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