Learn notes-hadoop Safe mode and directory snapshots

Safe Mode

1, namenode start, merge image and edit into new image, and generate a new edit log

2, the entire intelligent Safe mode, the client can only read

3. Check if Nameode is in safe mode

HDFs Dfsadmin-safemode Get//view Safe Mode

HDFs Dfsadmin-safemode Enter//Enter Safe mode

HDFs Dfsadmin-safemode Leave//Leave Safe Mode

HDFs Dfsadmin-safemode Wait//await Safe mode

4. Manually Save namespaces: Dfsadmin-savenamespace

5. Manually save the image file: HDFs dfsadmin-fetchimage

6. Save metadata: (Save under Hadoop_home: hadoop/logs/) HDFs Dfsadmin-metasave Xxx.dsds

7, start-balancer.sh: Start the Equalizer, the purpose of the cluster data storage on the more average, improve the performance of the entire cluster (in general, we are increasing the node

To start the equalizer in the case of a dot)

8. Hadoop Fs-count Statistics Directory

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Hadoop Snapshot Snapshot: It is to save the current picture. Generic directory The default scenario is that snapshots cannot be created. HDFs must be executed

Dfsadmin-allowsnapshot/user/ubuntu/data. Allow snapshots to be created followed by the address path where you want to create the snapshot. Here to allow

After the snapshot is created we can execute Adoop fs-createsnapshot/user/ubuntu/data snap-1 create the snapshot. Snap-1 is you create fast

Name it. View the snapshot of the word direct Hadoop fs-ls-r/user/ubuntu/data/.snapshot/. And if you're creating a snapshot, it's not forbidden.

With the snapshot

1. Create a snapshot of Hadoop FS [-createsnapshot <snapshotDir> [<snapshotname>]

2. Delete Snapshot Hadoop fs [-deletesnapshot<snapshotdir> <oldName> <newname>]

3. Rename Snapshot Hadoop fs [-renamesnappshot<snapshotdir> <oldName> <newname>]

4. Allow directory snapshot Hadoop dfsadmin [-allowsnapshot <snapshotdir>]

5. Disable directory snapshots Hadoop dfsamdin[-disallowsnapshot<snapshotdir>]

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Learn notes-hadoop Safe mode and directory snapshots