5.23.2.1 Restoring to Fewer Nodes Than the Original

You can restore to a cluster having fewer data nodes than the original provided that the larger number of nodes is an even multiple of the smaller number. In the following example, we use a backup taken on a cluster having four data nodes to a cluster having two data nodes.

1. The management server for the original cluster is on host host10. The original cluster has four data nodes, with the node IDs and host names shown in the following extract from the management server's config.ini file:

   [ndbd]
   NodeId=2
   HostName=host2
   
   [ndbd]
   NodeId=4
   HostName=host4
   
   [ndbd]
   NodeId=6
   HostName=host6
   
   [ndbd]
   NodeId=8
   HostName=host8

   We assume that each data node was originally started with ndbmtd --ndb-connectstring=host10 or the equivalent.

2. Perform a backup in the normal manner. See Section 6.8.2, “Using The NDB Cluster Management Client to Create a Backup”, for information about how to do this.

3. The files created by the backup on each data node are listed here, where N is the node ID and B is the backup ID.

   • BACKUP-B-0.N.Data

   • BACKUP-B.N.ctl

   • BACKUP-B.N.log

   These files are found under BackupDataDir/BACKUP/BACKUP-B, on each data node. For the rest of this example, we assume that the backup ID is 1.

   Have all of these files available for later copying to the new data nodes (where they can be accessed on the data node's local file system by ndb_restore). It is simplest to copy them all to a single location; we assume that this is what you have done.

4. The management server for the target cluster is on host host20, and the target has two data nodes, with the node IDs and host names shown, from the management server config.ini file on host20:

   [ndbd]
   NodeId=3
   hostname=host3
   
   [ndbd]
   NodeId=5
   hostname=host5

   Each of the data node processes on host3 and host5 should be started with ndbmtd -c host20 --initial or the equivalent, so that the new (target) cluster starts with clean data node file systems.

5. Copy two different sets of two backup files to each of the target data nodes. For this example, copy the backup files from nodes 2 and 4 from the original cluster to node 3 in the target cluster. These files are listed here:

   • BACKUP-1-0.2.Data

   • BACKUP-1.2.ctl

   • BACKUP-1.2.log

   • BACKUP-1-0.4.Data

   • BACKUP-1.4.ctl

   • BACKUP-1.4.log

   Then copy the backup files from nodes 6 and 8 to node 5; these files are shown in the following list:

   • BACKUP-1-0.6.Data

   • BACKUP-1.6.ctl

   • BACKUP-1.6.log

   • BACKUP-1-0.8.Data

   • BACKUP-1.8.ctl

   • BACKUP-1.8.log

   For the remainder of this example, we assume that the respective backup files have been saved to the directory /BACKUP-1 on each of nodes 3 and 5.

6. On each of the two target data nodes, you must restore from both sets of backups. First, restore the backups from nodes 2 and 4 to node 3 by invoking ndb_restore on host3 as shown here:

   $> ndb_restore -c host20 --nodeid=2 --backupid=1 --restore-data --backup-path=/BACKUP-1
   
   $> ndb_restore -c host20 --nodeid=4 --backupid=1 --restore-data --backup-path=/BACKUP-1

   Then restore the backups from nodes 6 and 8 to node 5 by invoking ndb_restore on host5, like this:

   $> ndb_restore -c host20 --nodeid=6 --backupid=1 --restore-data --backup-path=/BACKUP-1
   
   $> ndb_restore -c host20 --nodeid=8 --backupid=1 --restore-data --backup-path=/BACKUP-1