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.hdfs.server.datanode.FSDataset.FSVolume;
024    import org.apache.hadoop.util.DiskChecker.DiskOutOfSpaceException;
025    
026    public class RoundRobinVolumesPolicy implements BlockVolumeChoosingPolicy {
027    
028      private int curVolume = 0;
029    
030      @Override
031      public synchronized FSVolume chooseVolume(List<FSVolume> volumes, long blockSize)
032          throws IOException {
033        if(volumes.size() < 1) {
034          throw new DiskOutOfSpaceException("No more available volumes");
035        }
036        
037        // since volumes could've been removed because of the failure
038        // make sure we are not out of bounds
039        if(curVolume >= volumes.size()) {
040          curVolume = 0;
041        }
042        
043        int startVolume = curVolume;
044        long maxAvailable = 0;
045        
046        while (true) {
047          FSVolume volume = volumes.get(curVolume);
048          curVolume = (curVolume + 1) % volumes.size();
049          long availableVolumeSize = volume.getAvailable();
050          if (availableVolumeSize > blockSize) { return volume; }
051          
052          if (availableVolumeSize > maxAvailable) {
053            maxAvailable = availableVolumeSize;
054          }
055          
056          if (curVolume == startVolume) {
057            throw new DiskOutOfSpaceException(
058                "Insufficient space for an additional block. Volume with the most available space has "
059                    + maxAvailable
060                    + " bytes free, configured block size is "
061                    + blockSize);
062          }
063        }
064      }
065    
066    }