'Get disk type of the pool.'

def _get_disk_type(self, pool_name, result):

    pool_info = self.get_pool_info(pool_name, result)
    if (not pool_info):
        return None
    pool_disk = []
    for (i, x) in enumerate(['ssd', 'sas', 'nl_sas']):
        if (pool_info[('TIER%dCAPACITY' % i)] != '0'):
            pool_disk.append(x)
    if (len(pool_disk) > 1):
        pool_disk = ['mix']
    return (pool_disk[0] if pool_disk else None)
