Returns the pool that is the base tier for this pool.
The return value is the ID of the pool that should be used to read from/write to.
If tiering is not set up for the pool, returns \c pool.
@param cluster the cluster the pool is in
@param pool ID of the pool to query
@paramout base_tier base tier, or \c pool if tiering is not configured
@returns 0 on success, negative error code on failure
Returns the pool that is the base tier for this pool.
The return value is the ID of the pool that should be used to read from/write to. If tiering is not set up for the pool, returns \c pool.
@param cluster the cluster the pool is in @param pool ID of the pool to query @paramout base_tier base tier, or \c pool if tiering is not configured @returns 0 on success, negative error code on failure