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HDFS Snapshots are read-only point-in-time copies of the file system. Snapshots can be taken on a subtree of the file system or the entire file system.Snapshots are very efficient because they only copy data that are changed. We can restore the data to any previous snapshot. Some common use cases of snapshots are Data backup and Disaster recovery.

HDFS Snapshot Extension:

Falcon will support HDFS snapshot-based replication through HDFS Snapshot extension. Using this feature,

  • create and manage snapshots on source/target directories.
  • Mirror data from source to target for disaster recovery using these snapshots.
  • Perform retention on the snapshots created on source and target.

Snapshot replication will only work from single source directory to single target directory.

For snapshot to work, we expect users to do the following

  • ­Both source and target clusters must have a version of Hadoop 2.7.0 or higher.
  • The user submitting and scheduling the falcon extension should have permissions on both source and target directories.
  • Both directories should be snap shot­able.

To perform the HDFS Snapshot replication in Falcon, We need to create the source, target cluster entities and also need to create/give permissions to the staging and working directories. Please use the following steps to accomplish it.

Source Cluster:

hdfs dfs -rm -r /tmp/fs /tmp/fw
hdfs dfs -mkdir -p /tmp/fs
hdfs dfs -chmod 777 /tmp/fs
hdfs dfs -mkdir -p /tmp/fw
hdfs dfs -chmod 755 /tmp/fw
hdfs dfs -chown falcon /tmp/fs
hdfs dfs -chown falcon /tmp/fw

Target Cluster :

hdfs dfs -rm -r /tmp/fs /tmp/fw
hdfs dfs -mkdir -p /tmp/fs
hdfs dfs -chmod 777 /tmp/fs
hdfs dfs -mkdir -p /tmp/fw
hdfs dfs -chmod 755 /tmp/fw
hdfs dfs -chown falcon /tmp/fs
hdfs dfs -chown falcon /tmp/fw

Cluster Entities:

primaryCluster.xml

<?xml version="1.0" encoding="UTF-8"?>
<cluster xmlns="uri:falcon:cluster:0.1" colo="USWestOregon" description="oregonHadoopCluster" name="primaryCluster">
   <interfaces>
      <interface type="readonly" endpoint="webhdfs://mycluster1:20070" version="0.20.2" />
      <interface type="write" endpoint="hdfs://mycluster1:8020" version="0.20.2" />
      <interface type="execute" endpoint="primaryCluster-12.openstacklocal:8050" version="0.20.2" />
      <interface type="workflow" endpoint="http://primaryCluster-14.openstacklocal:11000/oozie" version="3.1" />
      <interface type="messaging" endpoint="tcp://primaryCluster-9.openstacklocal:61616?daemon=true" version="5.1.6" />
      <interface type="registry" endpoint="thrift://primaryCluster-14.openstacklocal:9083" version="0.11.0" />
   </interfaces>
   <locations>
      <location name="staging" path="/tmp/fs" />
      <location name="temp" path="/tmp" />
      <location name="working" path="/tmp/fw" />
   </locations>
   <ACL owner="ambari-qa" group="users" permission="0755" />
   <properties>
      <property name="dfs.namenode.kerberos.principal" value="nn/_HOST@EXAMPLE.COM" />
      <property name="hive.metastore.kerberos.principal" value="hive/_HOST@EXAMPLE.COM" />
      <property name="hive.metastore.sasl.enabled" value="true" />
      <property name="hadoop.rpc.protection" value="authentication" />
      <property name="hive.metastore.uris" value="thrift://primaryCluster-14.openstacklocal:9083" />
      <property name="hive.server2.uri" value="hive2://primaryCluster-14.openstacklocal:10000" />
   </properties>
</cluster>

falcon entity -submit -type cluster -file primaryCluster.xml --> primaryCluster

backupCluster :

<?xml version="1.0" encoding="UTF-8"?>
<cluster xmlns="uri:falcon:cluster:0.1" colo="USWestOregon" description="oregonHadoopCluster" name="backupCluster">
   <interfaces>
      <interface type="readonly" endpoint="webhdfs://mycluster2:20070" version="0.20.2" />
      <interface type="write" endpoint="hdfs://mycluster2:8020" version="0.20.2" />
      <interface type="execute" endpoint="backupCluster-5.openstacklocal:8050" version="0.20.2" />
      <interface type="workflow" endpoint="http://backupCluster-6.openstacklocal:11000/oozie" version="3.1" />
      <interface type="messaging" endpoint="tcp://backupCluster-1.openstacklocal:61616" version="5.1.6" />
      <interface type="registry" endpoint="thrift://backupCluster-6.openstacklocal:9083" version="0.11.0" />
   </interfaces>
   <locations>
      <location name="staging" path="/tmp/fs" />
      <location name="temp" path="/tmp" />
      <location name="working" path="/tmp/fw" />
   </locations>
   <ACL owner="ambari-qa" group="users" permission="0755" />
   <properties>
      <property name="dfs.namenode.kerberos.principal" value="nn/_HOST@EXAMPLE.COM" />
      <property name="hive.metastore.kerberos.principal" value="hive/_HOST@EXAMPLE.COM" />
      <property name="hive.metastore.sasl.enabled" value="true" />
      <property name="hadoop.rpc.protection" value="authentication" />
      <property name="hive.metastore.uris" value="thrift://backupCluster-6.openstacklocal:9083" />
      <property name="hive.server2.uri" value="hive2://backupCluster-6.openstacklocal:10000" />
   </properties>
</cluster>

falcon entity -submit -type cluster -file backupCluster.xml --> backupCluster

HDFS Snapshot Replication:

Source: [ Create directory and copy the data]

hdfs dfs -mkdir -p /tmp/falcon/HDFSSnapshot/source
hdfs dfs -put NYSE-2000-2001.tsv /tmp/falcon/HDFSSnapshot/source

Note: you can download the NYSE-2000-2001.tsv file from

https://s3.amazonaws.com/hw-sandbox/tutorial1/NYSE-2000-2001.tsv.gz

Allow Snapshot to the directory:

ddfs dfsadmin -allowSnapshot /tmp/falcon/HDFSSnapshot/source [ hdfs]
hdfs lsSnapshottableDir [ ambari-qa]

Target Cluster

hdfs dfs -mkdir -p /tmp/falcon/HDFSSnapshot/target
hdfs dfsadmin -allowSnapshot /tmp/falcon/HDFSSnapshot/target

hdfs-snapshot.properties

jobName=HDFSSnapshot
jobClusterName=primaryCluster
jobValidityStart=2016-05-09T06:25Z
jobValidityEnd=2016-05-09T08:00Z
jobFrequency=days(1)
sourceCluster=primaryCluster
sourceSnapshotDir=/tmp/falcon/HDFSSnapshot/source
sourceSnapshotRetentionAgeLimit=days(1)
sourceSnapshotRetentionNumber=3
targetCluster=backupCluster
targetSnapshotDir=/tmp/falcon/HDFSSnapshot/target
targetSnapshotRetentionAgeLimit=days(1)
targetSnapshotRetentionNumber=3
jobAclOwner=ambari-qa
jobAclGroup=users
jobAclPermission="0x755"

Submit And schedule the job using the property file:

falcon extension -extensionName hdfs-snapshot-mirroring -submitAndSchedule -file hdfs-snapshot.properties

By using the jobName we can find the oozie job it has launched

falcon extension -instances -jobName HDFSSnapshot 

Once the job is completed, we can see in source the snapshot will be automatically created and snapshot along with source content are replicated in the target cluster :

Source Cluster HDFS Content:

hdfs dfs -ls -R hdfs://mycluster1:8020//tmp/falcon/HDFSSnapshot/source/

drwxr-xr-x - ambari-qa hdfs 0 2016-10-25 02:27 hdfs://mycluster1:8020/tmp/falcon/HDFSSnapshot/source/source -rw-r--r-- 3 ambari-qa hdfs 44005963 2016-10-25 02:27 hdfs://mycluster1:8020/tmp/falcon/HDFSSnapshot/source/source/NYSE-2000-2001.tsv 

Target Cluster HDFS Content:

hdfs dfs -ls -R hdfs://mycluster2:8020//tmp/falcon-HDFSSnapshot/target/

drwxr-xr-x - ambari-qa hdfs 0 2016-10-25 02:28 hdfs://mycluster2:8020/tmp/falcon/HDFSSnapshot/target/source -rw-r--r-- 3 ambari-qa hdfs 44005963 2016-10-25 02:28 hdfs://mycluster2:8020/tmp/falcon/HDFSSnapshot/target/source/NYSE-2000-2001.tsv

We can see the data has been replicated from source to target cluster.

Source Snapshot Directory:

hdfs dfs -ls hdfs://mycluster1:8020//tmp/falcon/HDFSSnapshot/source/.snapshot

Found 1 items drwxr-xr-x - ambari-qa hdfs 0 2016-10-25 02:27 hdfs://mycluster1:8020/tmp/falcon/HDFSSnapshot/source/.snapshot/falcon-snapshot-HDFSSnapshot-2016-05-09-06-25-1477362461509 

Target Snapshot Directory:

hdfs dfs -ls hdfs://mycluster2:8020//tmp/falcon/HDFSSnapshot/target/.snapshot

Found 1 itemsdrwxr-xr-x   - ambari-qa hdfs          0 2016-10-25 02:28 hdfs://mycluster2:8020/tmp/falcon/HDFSSnapshot/target/.snapshot/falcon-snapshot-HDFSSnapshot-2016-05-09-06-25-1477362461509

We can see the snapshot directory has been automatically created in source and also replicated from source to target cluster.

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Comments
New Contributor

Thanks for sharing! whenever there is a change in the source directory, is there a corresponding update on the target directory? @Murali Ramasami

Contributor

@zhixun he Yes. Whenever there is a change, snapshot will get created in source and falcon process instance will trigger based on the frequency

Contributor

Quick question, curious of perspective, does it make sense to use falcon snapshot support to just manage the snapshots for a single cluster and not necessarily the DR replication aspects.

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‎10-25-2016 05:29 PM
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