Known Issues in HDFS

Learn about the known issues in HDFS, the impact or changes to the functionality, and the workaround.

CDPD-67230: Rolling restart can cause failed writes on small clusters

In a rolling restart, if the cluster has less than 10 datanodes existing writers can fail with an error indicating a new block cannot be allocated and all nodes are excluded. This is because you have attempted to use all the datanodes in the cluster, and failed to write to each of them as they were restarted. This only happen on small clusters of less than 10 datanodes, because larger clusters have more spare nodes to allow the write to continue.

None.

CDPD-60873: java.io.IOException:Encountered "status=ERROR, status message, ack with firstBadLink" while fixing the HDFS corrupt file during rollback.

Increase the value of dfs.client.block.write.retries to the number of nodes in the cluster and perform Deploy client configuration procedure for rectification.

CDPD-60431: Configuration difference between 7.1.7 SP2 and 7.1.9.0 results

Component	Configuration	Old Value	New Value	Description
HDFS	dfs.permissions.ContentSummary.subAccess	Not set	True	Performance optimization for NameNode content summary API
HDFS	dfs.datanode.handler.count	3	10	Optimal value for DN server threads on large clusters

None.

CDPD-60387: Configuration difference between 7.1.8.3 and 7.1.9.0 results

Component	Configuration	Old Value	New Value	Description
HDFS	dfs.namenode.accesstime.precision	Not set	0	Optimal value for NameNode performance on large clusters
HDFS	dfs.datanode.handler.count	3	10	Optimal value for DN server threads on large clusters

None.

OPSAPS-64307: When the JournalNodes on a cluster are restarted, the Add new NameNode wizard for HDFS service might fail to bootstrap the new NameNode. If there was no new fsImage created from the time JournalNodes restarted, during the restart the edit logs were rolled in the system.

If the bootstraping fails during the Add new NameNode wizard, then perform the following steps:

1. Delete the newly added NameNode and FailoverController
2. Move the active HDFS NameNode to safe mode
3. Perform the Save Namespace operation on the active HDFS NameNode
4. Leave safe mode on the active HDFS NameNode
5. Add the new NameNode again

OPSAPS-64363: Deleting of additional Standby Namenode does not delete the ZKFC role and this has to be done manually.

None.

CDPD-28390: Rolling restart of the HDFS JournalNodes may time out on Ubuntu20.

If the restart operation times out, you can manually stop and restart the Name Node and Journal Node services one by one.

OPSAPS-55788: WebHDFS is always enabled. The Enable WebHDFS option does not take effect.

None.

OPSAPS-63299: Disable HA command for a nameservice does not work if the nameservice has more than 2 NameNodes defined.

None.

OPSAPS-63301: Deleting nameservice command does not delete all the NameNodes belonging to the nameservice, if there are more than two NameNodes that are assigned to the nameservice.

None.

Unsupported features

The following HDFS features are currently not supported in Cloudera Data Platform:

• ACLs for the NFS gateway (HADOOP-11004)
• Aliyun Cloud Connector (HADOOP-12756)
• Allow HDFS block replicas to be provided by an external storage system (HDFS-9806)
• Consistent standby Serving reads (HDFS-12943)
• Cost-based RPC FairCallQueue (HDFS-14403)
• HDFS Router Based Federation (HDFS-10467)
• NameNode Federation (HDFS-1052)
• NameNode Port-based Selective Encryption (HDFS-13541)
• Non-Volatile Storage Class Memory (SCM) in HDFS Cache Directives (HDFS-13762)
• OpenStack Swift (HADOOP-8545)
• SFTP FileSystem (HADOOP-5732)
• Storage policy satisfier (HDFS-10285)