my $parser = new XML::LibXML;

my $tree = $parser->parse_file('935.xml');
my $root = $tree->getDocumentElement;
my @symm_tree    = $root->getChildrenByTagName('Symmetrix') or croak;
for my $symm_tree ( @symm_tree ) {
    my @devices_tree = $symm_tree->getChildrenByTagName('Device') or croak;

    my $device_num;
    for my $device_tree ( @devices_tree ) {
        $device_num++;
        my @devinfo_tree    = $device_tree->getChildrenByTagName('Dev_Info') or croak;
        my @capacity_tree      = $device_tree->getChildrenByTagName('Capacity') or croak;

        my $dev_name; # key

        for my $devinfo_tree ( @devinfo_tree ) {
            $dev_name = $devinfo_tree->getChildrenByTagName('dev_name');
            my $dev_cnfg = $devinfo_tree->getChildrenByTagName('configuration');

            $conf_of{$dev_name} .= $dev_cnfg;
        }

        for my $capacity_tree ( @capacity_tree ) {
            my $cyls = $capacity_tree->getChildrenByTagName('cylinders');
            $conf_of{$dev_name} .= $cyls;
        }
    }
}