| Interface | Description | 
|---|---|
| BlockStatsMXBean | This is an interface used to retrieve statistic information related to
 block management. | 
| DatanodeAdminMonitorInterface | Interface used to implement a decommission and maintenance monitor class,
 which is instantiated by the DatanodeAdminManager class. | 
| DatanodeStatistics | Datanode statistics | 
| Class | Description | 
|---|---|
| AvailableSpaceBlockPlacementPolicy | Space balanced block placement policy. | 
| AvailableSpaceRackFaultTolerantBlockPlacementPolicy | Space balanced rack fault tolerant block placement policy. | 
| BlockIdManager | BlockIdManager allocates the generation stamps and the block ID. | 
| BlockInfoStriped.StorageAndBlockIndex | This class contains datanode storage information and block index in the
 block group. | 
| BlockManagerFaultInjector | Used to inject certain faults for testing. | 
| BlockPlacementPolicyWithNodeGroup | The class is responsible for choosing the desired number of targets
 for placing block replicas on environment with node-group layer. | 
| BlockPlacementStatusDefault | |
| BlockStoragePolicySuite | A collection of block storage policies. | 
| BlockUnderConstructionFeature | Represents the under construction feature of a Block. | 
| CombinedHostFileManager | This class manages datanode configuration using a json file. | 
| DatanodeAdminBackoffMonitor | This class implements the logic to track decommissioning and entering
 maintenance nodes, ensure all their blocks are adequately replicated
 before they are moved to the decommissioned or maintenance state. | 
| DatanodeAdminDefaultMonitor | Checks to see if datanodes have finished DECOMMISSION_INPROGRESS or
 ENTERING_MAINTENANCE state. | 
| DatanodeAdminMonitorBase | This abstract class provides some base methods which are inherited by
 the DatanodeAdmin BackOff and Default Monitors, which control decommission
 and maintenance mode. | 
| DatanodeDescriptor.CachedBlocksList | A list of CachedBlock objects on this datanode. | 
| DatanodeStorageInfo | A Datanode has one or more storages. | 
| HostFileManager | This class manages the include and exclude files for HDFS. | 
| HostSet | The HostSet allows efficient queries on matching wildcard addresses. | 
| NumberReplicas | A immutable object that stores the number of live replicas and
 the number of decommissioned Replicas. | 
| ProvidedStorageMap.ProvidedDescriptor | An abstract DatanodeDescriptor to track datanodes with provided storages. | 
| SlowDiskTracker.DiskLatency | This structure is a thin wrapper over disk latencies. | 
| Enum | Description | 
|---|---|
| CorruptReplicasMap.Reason | The corruption reason code | 
| DatanodeDescriptor.CachedBlocksList.Type | |
| NumberReplicas.StoredReplicaState | 
| Exception | Description | 
|---|---|
| UnresolvedTopologyException | This exception is thrown if resolving topology path 
 for a node fails. | 
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