Returns devices data.

def devices_data():
    """Returns devices data.
    """
    response = {}
    for part in psutil.disk_partitions():
        device = part.device
        response[device] = {
            'device': device,
            'mountpoint': part.mountpoint,
            'fstype': part.fstype,
            'opts': part.opts,
        }
        if part.mountpoint:
            usage = psutil.disk_usage(part.mountpoint)
            response[device]['usage'] = {
                'size': mark(usage.total, 'bytes'),
                'used': mark(usage.used, 'bytes'),
                'free': mark(usage.free, 'bytes'),
                'percent': mark(usage.percent, 'percentage')
            }
    return response