Hello, I've done some initial work for making the volume-block choosing policy pluggable (so that methods other than round-robin may be provided).
The following is my initial interface design, and am looking for comments/critique/etc. w.r.t. https://issues.apache.org/jira/browse/HDFS-1120's scope, before I start pushing out some tests + patches: /************************************************** * BlockVolumeChoosingPolicy allows a DataNode to * specify what policy is to be used while choosing * a volume for a block request. * ***************************************************/ public interface BlockVolumeChoosingPolicy extends Configurable { /** * Returns a specific FSVolume after applying a suitable choice algorithm * to place a given block, given a list of FSVolumes and the block * size sought for storage. * @param volumes - the array of FSVolumes that are available. * @param blockSize - the size of the block for which a volume is sought. * @return the chosen volume to store the block. * @throws IOException when disks are unavailable or are full. */ public FSVolume chooseVolume(FSVolume[] volumes, long blockSize) throws IOException; } This can be neatly used within FSVolumeSet.getNextVolume() [Maybe this too needs to be renamed, since it may not make sense as 'next' once it becomes pluggable] Looking forward to a discussion. -- Harsh J http://harshj.com
