Managing database tables in WordPress multisite

use the API, the functions of WordPress for save data and check before, it is an Multisite install; thats all. The first example is only for check, is the activated as network wide.

// if is active in network of multisite
if ( is_multisite() && isset($_GET['networkwide']) && 1 == $_GET['networkwide'] ) {
    add_site_option( 'my_settings_id', $data );
} else {
    add_option( 'my_settings_id', $data );
}

The follow example check for mutlisite and if the plugin active in complete network.

if ( is_multisite() && is_plugin_active_for_network( plugin_basename( __FILE__ ) ) )
    $values = get_site_option( 'my_settings_id' );
else
    $values = get_option( 'my_settings_id' );

Also you can check this in each blog and save the data in the tables of each blog.

*the examples was from this post