How Backup Recovers Data

When Backup receives a recover request from a client, the server's nsrd daemon contacts the server's nsrmmd media daemon. The nsrmmd daemon contacts the server's nsrmmdbd media database daemon to determine which media contain the save set requested by recover. After the save set's media location is obtained, nsrmmd issues a mount request, the media is positioned to the beginning of the save set, and the save set stored on the mounted media is passed to nsrmmd. The media daemon forwards the save set to the client's recover program, which restores the data to the client's filesystem.

When the server's nsrmmdbd media database daemon cannot locate the required volumes, or when there are no nsrmmd daemons (enabled devices) on the Backup storage node or server, the recover request fails. Backup displays the following message on the client machine that requested the recover:

NSR server client: no matching devices on server-or-storage-node 

Backup also displays the following message in the Pending display for the Backup server:

media notice: no matching devices on server-or-storage-node for recover
by client client
media notice: enable or check device(s) on server-or-storage-node

Figure A-2 shows how the Backup server and client daemons and programs interact while recovering data to a Backup client.

Figure A-2 How Backup Daemons and Programs Interact During a Recover Session

Backup Operations With Storage Nodes

A storage node is a machine that contains Backup client and media management daemons and programs. A storage node is connected to one or more storage devices that are used in Backup operations, such as backup and recovery. Media management daemons on the storage node machine read and write data on storage volumes.

Backup and recover operations with storage nodes are very similar to backup and recover operations on the Backup server. The major difference is where the data resides.

A storage node is controlled by a Backup server. The Backup server's nsrd master daemon starts the nsrmmd, media management daemon, on the storage node, and during backup, the Backup server routes appropriate data to each media management daemon according to the Storage Node Affinity attribute in the Clients resource.

After data is written to the storage devices connected to storage node machines (remote devices), the Backup server tracks the location of the data. On the Backup server, the nsrindexd daemon writes entries in the client file indexes to track the location of each file in a save set, and the nsrmmdbd daemon writes entries in the media database to track the location of each save set on media.

Figure A-3 shows how the Backup server, client, and storage node daemons and programs interact during a scheduled save in a Backup setup that includes a storage node and a remote storage device.

Figure A-3 How Backup Daemons and Programs Interact During a Save Session With a Storage Node

When the Backup server receives a request from the client's recover program, it contacts nsrmmd, the media management daemon, on the storage node instead of on the server machine. The nsrmmd daemon reads the data from media and sends the data to the Backup client, where the recover program rebuilds the data.

Figure A-4 shows an example of how a recover process works in a Backup setup that includes a storage node and a remote storage device.

Figure A-4 How Backup Daemons and Programs Interact During a Recover Session With a Storage Node