Recovering NameNode Data

Scenario

NameNode data needs to be recovered in the following scenarios: HDFS metadata is modified or deleted unexpectedly and needs to be restored. After a MRS cluster administrator performs critical data adjustment in NameNode, an exception occurs or the operation has not achieved the expected result. All modules are faulty and become unavailable. Data is migrated to a new cluster.

MRS cluster administrators can create a recovery task in FusionInsight Manager to recover NameNode data. Only manual recovery tasks are supported.

Data recovery can be performed only when the system version is consistent with that of data backup.
To recover data when the service is running properly, you are advised to manually back up the latest management data before recovering data. Otherwise, the NameNode data that is generated after the data backup and before the data recovery will be lost.
It is recommended that a data restoration task restore the metadata of only one component to prevent the data restoration of other components from being affected by stopping a service or instance. If data of multiple components is restored at the same time, data restoration may fail.
HBase metadata cannot be restored at the same time as NameNode metadata. As a result, data restoration fails.

Impact on the System

After the data is recovered, the data produced between the backup time and restoration time is lost.
After the data is recovered, the NameNode needs to be restarted and is unavailable during the restart.
After data is restored, metadata and service data may not be matched, HDFS enters the security mode, and the HDFS service cannot be started.

Prerequisites

To restore data from the remote HDFS, you need to prepare the standby cluster. If the active cluster is deployed in security mode and the active and standby clusters are not managed by the same FusionInsight Manager, configure system mutual trust. For details, see Configuring Cross-Manager Cluster Mutual Trust Relationships. If the active cluster is deployed in normal mode, do not configure mutual trust.

Cross-cluster replication has been configured for the active and standby clusters. For details, see Enabling Cross-Cluster Replication.
The time of the active cluster and standby cluster must be the same, and the NTP service in the active and standby clusters must use the same time source.
You have logged in to FusionInsight Manager. For details, see Logging In to FusionInsight Manager.
On FusionInsight Manager, all the NameNode role instances whose data is to be recovered are stopped. Other HDFS role instances must keep running. After data is recovered, the NameNode role instances need to be restarted. The NameNode role instances cannot be accessed during the restart.
The NameNode backup files are stored Data path/LocalBackup/ on the active management node.

Procedure

Choose Cluster > Name of the desired cluster > Services > HDFS > Instance > NameNode to check whether the NameNode instances of the data to be restored are stopped. If the NameNode instances are not stopped, stop them.
On FusionInsight Manager, choose O&M > Backup and Restoration > Backup Management.
In the Operation column of a specified task in the task list, click More > View History to view historical backup task execution records.

In the displayed window, locate a specified success record and click View in the Backup Path column to view the backup path information of the task and find the following information:
- Backup Object specifies the data source of the backup data.
- Backup Path specifies the full path where the backup files are saved.
  Select the correct item, and manually copy the full path of backup files in Backup Path.
On FusionInsight Manager, choose O&M > Backup and Restoration > Restoration Management.
Click Create.
Set Task Name to the name of the recovery task.
Select the cluster to be operated from Recovery Object.
Select NameNode.
Set Path Type of NameNode to a backup directory type.

The settings vary according to backup directory types:
- LocalDir: indicates that the backup files are stored on the local disk of the active management node.
  If you select this value, you need to set the following parameters:
  - Source Path: indicates the full path of the local disk for storing standby cluster backup data. For example, backup path/backup task name_data source_task creation time/version_data source_task execution time.tar.gz.
  - Target NameService Name: indicates the target NameService that corresponds to the selected backup directory. The default value of this parameter is hacluster.
- RemoteHDFS(DistCp): indicates that the backup files are stored in the HDFS directory of the standby cluster.
  If you select this value, you need to set the following parameters:
  - Source NameService Name: indicates the NameService name of the backup data cluster. You can set it to the NameService name (haclusterX, haclusterX1, haclusterX2, haclusterX3, or haclusterX4) of the built-in remote cluster of the cluster, or the NameService name of a configured remote cluster.
  - IP Mode: mode of the target IP address.The system automatically selects the IP address mode based on the cluster network type, for example, IPv4 or IPv6.
  - Source NameNode IP Address: indicates the NameNode service plane IP address of the standby cluster, supporting the active node or standby node.
  - Source Path: indicates the full path of the HDFS directory for storing standby cluster backup data. For example, backup path/backup task name_data source_task creation time/version_data source_task execution time.tar.gz.
  - Queue Name: indicates the name of the Yarn queue used for backup task execution. The name must be the same as the name of the queue that is running properly in the cluster.
  - Target NameService Name: indicates the target NameService that corresponds to the selected backup directory. The default value of this parameter is hacluster.
- NFS: indicates that backup files are stored in the NAS over the NFS protocol.
  If you select NFS, set the following parameters:
  - IP Mode: mode of the target IP address.The system automatically selects the IP address mode based on the cluster network type, for example, IPv4 or IPv6.
  - Server IP address: indicates the NAS server IP address.
  - Source Path: indicates the complete path of the backup file on the NAS server. For example, backup path/backup task name_data source_task creation time/version_data source_task execution time.tar.gz.
  - Target NameService Name: indicates the target NameService that corresponds to the selected backup directory. The default value of this parameter is hacluster.
- CIFS: indicates that backup files are stored in the NAS over the CIFS protocol.
  If you select CIFS, set the following parameters:
  - IP Mode: mode of the target IP address.The system automatically selects the IP address mode based on the cluster network type, for example, IPv4 or IPv6.
  - Server IP address: indicates the NAS server IP address.
  - Port: indicates the port ID used by the CIFS protocol to connect to the NAS server. The default value is 445.
  - Username: Indicates the user name that is configured when setting the CIFS protocol.
  - Password: indicates the password that is configured when setting the CIFS protocol.
  - Source Path: indicates the complete path of the backup file on the NAS server. For example, backup path/backup task name_data source_task creation time/version_data source_task execution time.tar.gz.
  - Target NameService Name: indicates the target NameService that corresponds to the selected backup directory. The default value of this parameter is hacluster.
- SFTP: Indicates that backup files are stored in the server using SFTP.
  If you select SFTP, set the following parameters:
  - IP Mode: mode of the target IP address.The system automatically selects the IP address mode based on the cluster network type, for example, IPv4 or IPv6.
  - Server IP address: Enter the IP address of the server where the backup data is stored.
  - Port: Enter the port number used by the SFTP protocol to connect to the backup server. The default value is 22.
  - Username: Enter the username for connecting to the server using SFTP.
  - Password: Enter the password for connecting to the server using SFTP.
  - Source Path: Enter the full path of the backup file on the backup server. For example, backup path/backup task name_data source_task creation time/version_data source_task execution time.tar.gz.
  - Target NameService Name: indicates the target NameService that corresponds to the selected backup directory. The default value of this parameter is hacluster.
- OBS: indicates that the backup files are stored in the OBS directory.
  If you select this value, you need to set the following parameters:
  - Source Path: indicates the full path for storing backup data in OBS. For example, backup path/backup task name_data source_task creation time/version_data source_task execution time.tar.gz.
  - Target NameService Name: indicates the target NameService that corresponds to the selected backup directory. The default value of this parameter is hacluster.
    
    MRS 3.1.0 and later versions support saving backup files to OBS.
Click OK to save the settings.
In the recovery task list, locate a created task and click Start in the Operation column to execute the recovery task.
- After the recovery is successful, the progress bar is in green.
- After the recovery is successful, the recovery task cannot be executed again.
- If the recovery task fails during the first execution, rectify the fault and click Retry to execute the task again.
On FusionInsight Manager, choose Cluster > Name of the desired cluster > Services > HDFS > More > Restart Service.

In the displayed window, enter the password of the current user and click OK. After the system displays "Operation succeeded", click Finish. The service is successfully started.