001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.hadoop.hdfs.server.datanode;
019    
020    import java.io.IOException;
021    import java.util.List;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import org.apache.hadoop.classification.InterfaceStability;
025    import org.apache.hadoop.hdfs.server.datanode.FSDataset.FSVolume;
026    
027    /**************************************************
028     * BlockVolumeChoosingPolicy allows a DataNode to
029     * specify what policy is to be used while choosing
030     * a volume for a block request.
031     * 
032     ***************************************************/
033    @InterfaceAudience.Public
034    @InterfaceStability.Evolving
035    public interface BlockVolumeChoosingPolicy {
036    
037      /**
038       * Returns a specific FSVolume after applying a suitable choice algorithm
039       * to place a given block, given a list of FSVolumes and the block
040       * size sought for storage.
041       * 
042       * (Policies that maintain state must be thread-safe.)
043       * 
044       * @param volumes - the array of FSVolumes that are available.
045       * @param blockSize - the size of the block for which a volume is sought.
046       * @return the chosen volume to store the block.
047       * @throws IOException when disks are unavailable or are full.
048       */
049      public FSVolume chooseVolume(List<FSVolume> volumes, long blockSize)
050        throws IOException;
051    
052    }