# Package org.apache.hadoop.hdfs.server.datanode.fsdataset

- Interface Summary
  Interface | Description
  --- | ---
  FsVolumeReference | This holds volume reference count as AutoClosable resource.
  FsVolumeSpi | This is an interface for the underlying volume.
  FsVolumeSpi.BlockIterator | BlockIterator will return ExtendedBlock entries from a block pool in this volume.

- Class Summary
  Class | Description
  --- | ---
  AvailableSpaceVolumeChoosingPolicy<V extends FsVolumeSpi> | A DN volume choosing policy which takes into account the amount of free space on each of the available volumes when considering where to assign a new replica allocation.
  FsDatasetSpi.Factory<D extends org.apache.hadoop.hdfs.server.datanode.fsdataset.FsDatasetSpi<?>> | A factory for creating `FsDatasetSpi` objects.
  FsDatasetSpi.FsVolumeReferences | It behaviors as an unmodifiable list of FsVolume.
  FsVolumeSpi.ScanInfo | Tracks the files and other information related to a block on the disk Missing file is indicated by setting the corresponding member to null.
  FsVolumeSpi.VolumeCheckContext | Context for the `Checkable.check(K)` call.
  LengthInputStream | An input stream with length.
  ReplicaInputStreams | Contains the input streams for the data and checksum of a replica.
  ReplicaOutputStreams | Contains the output streams for the data and checksum of a replica.
  RoundRobinVolumeChoosingPolicy<V extends FsVolumeSpi> | Choose volumes with the same storage type in round-robin order.

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