How Backup Backs Up Data

Backup calls upon several daemons and programs when a request for a backup is received. The daemons coordinate the tasks associated with a backup or recovery and record information about what was backed up and the media containing the backed-up data.

Backup Daemons and Programs

This section provides a description of the Backup server and storage node daemons and programs, which contact the client for a backup and maintain the server's client file index and media databases. (For more information about storage nodes, see "Backup Operations With Storage Nodes ".) The Backup man pages contain further details about the Backup daemons and programs. Table A-1 describes the server daemons and programs.

Table A-1 Functions of Server Daemons and Programs

Daemon/Program	Function
ansrd	This daemon monitors an active save or recover session; agent process spawned by nsrd in response to a save or recover session.
asavegrp	This daemon monitors the progress of individual save sets; agent process invoked by savegrp.
nsrck	This daemon checks the consistency of the client file index; invoked by nsrd whenever the consistency of the client file index needs to be confirmed.
nsrd	This daemon provides an RPC-based save and recover service to Backup clients; master Backup daemon.
nsrim	This daemon automatically manages the server's client file index; invoked at the end of a savegrp.
nsrindexd	This daemon provides a method for inserting entries in the client file index based on information passed by the save program.
nsrmmd	This daemon provides device support, generates mount requests, and multiplexes save set data during a multi-client backup (nsrd can start several nsrmmd daemons, up to the number specified in the device's Target Sessions attribute); media multiplexor daemon.
nsrmmdbd	This daemon provides media and save set database management services to the local nsrd and nsrmmd daemons and records entries in the media database; media management database daemon.
savegrp	This program runs a group of Backup clients through the save process.

The nsrd master Backup server daemon is responsible for several tasks:

• Starting other daemons

• Allocating media daemons on server and storage node machines

• Authorizing backup and recover services for the client

• Contacting clients for scheduled backups

• Maintaining Backup configuration information

• Monitoring backup and recover sessions

• Maintaining server statistics and message logs

The nsrd Backup server daemon calls on the nsrexecd Backup client daemon and several client-side programs when it receives a scheduled or on-demand backup request. The ansrd temporary server agent daemon starts on the Backup server to monitor the progress of the backup session. Table A-2 describes the client-side daemons and programs.

Table A-2 Functions of Client Daemons and Programs

Daemon/Program	Function
nsrexecd	This daemon authenticates the Backup server's remote execution request and executes the save and savefs commands on the client.
recover	This program browses the Backup server's client file index and restores the specified file to primary disk storage.
save	This program sends specified files in a multiplexed data stream to the Backup server for backup to media by nsrmmd and entry in the client file indexes and media database by nsrindexd.
savefs	This program sends information about the save sets to back up for the client; identifies save set data modified since the previous level save.

Events During a Scheduled Backup

When you configure a backup group on the Backup server, you schedule a start time for the backup group. The nsrd server daemon starts the server's savegrp program for the backup group at the scheduled time.

The savegrp program queries the client resources configured on the Backup server to determine:

• Which clients configured on the server are members of the scheduled group

• What level of backup (save) to perform

  How many save sets to run concurrently, determined by the parallelism value set on the Backup server

• When the most recent backup of the group occurred

If any of this information is not available on the Backup server, savegrp sends a request to the nsrexecd client-side daemon to run savefs on each client assigned to the backup group to gather the necessary details.

The savefs program tells savegrp which objects to back up for the client. After savegrp receives information about the objects to back up, savegrp assembles a work list for the server. The work list specifies the order in which clients are contacted for backup. The order of the work list is determined by the Client Priority attribute in the Clients resource. The client with the lowest value in the Client Priority attribute is contacted first.

If problems were encountered with the client file index during the previous backup session, nsrd invokes the nsrck daemon to check the consistency and state of the Backup server's client file indexes and media database. Then, nsrd starts the nsrindexd client file index insertion daemon.

The savegrp program contacts the first client on the server's work list. The client's nsrexecd is invoked and starts a save session of the first save set listed on the server's work list. The save program passes to nsrd all save criteria, such as group, client, save sets, storage node affinity, and level of the save data. With this information, nsrd determines the pool of volumes that will store the data and forwards the information to the appropriate media daemon, on either the Backup server or on a storage node controlled by the Backup server.

The nsrmmd media daemon:

• Sends a message to the console of the Backup server, requesting a mount of the media assigned to the volume pool indicated by nsrd

• Writes the data sent by save to storage media

• Forwards storage information to nsrmmdbd for recording in the Backup server's media database

Any time there is a lull in save set activity from the client, the Backup server attempts to find another save set in the group to keep the process moving. The savegrp program attempts to concurrently back up as many save sets as possible, up to the limit set by the parallelism attribute in the Backup server's configuration, to use the backup devices to their maximum potential.

The savegrp program repeats the process for each item on the server's work list until all clients in the group are backed up. Before the savegrp is completed, if the Backup server is part of the group being backed up or the server is not part of any enabled group, nsrim is invoked and the Backup server's bootstrap file is backed up. When the bootstrap backup is completed, a bootstrap printout is sent to the default printer configured for the Backup server. Keep the bootstrap printout in a safe place in case you need to restore the Backup server.

The final results of the savegrp execution are sent back to the server and are included in the savegroup completion report, which is sent through email to root.

Figure A-1 shows how all the Backup client and server daemons and programs interact during a scheduled save.

Figure A-1 How Backup Daemons and Programs Interact During a Scheduled Save