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Administrator's Guide


How Tivoli Storage Manager Stores Client Data

Tivoli Storage Manager policies are rules that determine how the client data is stored and managed. The rules include where the data is initially stored, how many backup versions are kept, how long archive copies are kept, and so on. You can have multiple policies and assign the different policies as needed to specific clients, or even to specific files.

Policy assigns a location in server storage where data is initially stored. Server storage is divided into storage pools that are groups of storage volumes. Server storage can include hard disk, optical, and tape volumes.

When you install Tivoli Storage Manager, you have a default policy that you can use. For details about this default policy, see The Standard Policy. You can modify this policy and define other policies.

Clients use Tivoli Storage Manager to store data for any of the following purposes:

Backup and restore
The backup process copies data from client workstations to server storage to ensure against loss of data that is regularly changed. The server retains versions of a file according to policy, and replaces older versions of the file with newer versions. Policy includes the number of versions and the retention time for versions.

A client can restore the most recent version of a file, or can restore earlier versions.

Archive and retrieve
The archive process copies data from client workstations to server storage for long-term storage. The process can optionally delete the archived files from the client workstations. The server retains archive copies according to the policy for archive retention time. A client can retrieve an archived copy of a file.

Instant archive and rapid recovery
Instant archive is the creation of a complete set of backed-up files for a client. The set of files is called a backup set. A backup set is created on the server from the most recently backed-up files that are already stored in server storage for the client. Policy for the backup set consists of the retention time that you choose when you create the backup set.

You can copy a backup set onto compatible portable media, which can then be taken directly to the client for rapid recovery without the use of a network and without having to communicate with the Tivoli Storage Manager server.

Migration and recall
Migration, a function of the Tivoli Space Manager program, frees up client storage space by copying files from workstations to server storage. On the client, the Tivoli Space Manager program replaces the original file with a stub file that points to the original in server storage. Files are recalled to the workstations when needed.

This process is also called hierarchical storage management (HSM). Once configured, the process is transparent to the users. Files are migrated and recalled automatically.

Policy determines when files are considered for automatic migration. On the UNIX systems that support the Tivoli Space Manager program, policies determine whether files must be backed up to the server before being migrated. Space management is also integrated with backup. If the file to be backed up is already migrated to server storage, the file is backed up from there.

Figure 1 shows how policy is part of the Tivoli Storage Manager process for storing client data.

Figure 1. How Tivoli Storage Manager Controls Backup, Archive, and Migration Processes

How Tivoli Storage Manager Controls Backup, Archive, and Migration

The steps in the process are as follows:

(1) A client initiates a backup, archive, or migration operation. The file involved in the operation is bound to a management class. The management class is either the default or one specified for the file in client options (the client's include-exclude list).

(2) If the file is a candidate for backup, archive, or migration based on information in the management class, the client sends the file and file information to the server.

(3) The server checks the management class that is bound to the file to determine the destination, the name of the Tivoli Storage Manager storage pool where the server initially stores the file. For backed-up and archived files, destinations are assigned in the backup and archive copy groups, which are within management classes. For space-managed files, destinations are assigned in the management class itself.

The storage pool can be a group of disk volumes, tape volumes, or optical volumes.

(4) The server stores the file in the storage pool that is identified as the storage destination.

The Tivoli Storage Manager server saves information in its database about each file that it backs up, archives, or migrates.

If you set up server storage in a hierarchy, Tivoli Storage Manager can later migrate the file to a storage pool different from the one where the file was initially stored. For example, you may want to set up server storage so that Tivoli Storage Manager migrates files from a disk storage pool to tape volumes in a tape storage pool.

Files remain in server storage until they expire and expiration processing occurs, or until they are deleted from server storage. A file expires because of criteria that are set in policy. For example, the criteria include the number of versions allowed for a file and the number of days that have elapsed since a file was deleted from the client's file system.

For information on assigning storage destinations in copy groups and management classes, and on binding management classes to client files, see Chapter 12, Implementing Policies for Client Data.

For information on managing the database, see Chapter 18, Managing the Database and Recovery Log.

For information about storage pools and storage pool volumes, see Chapter 9, Managing Storage Pools and Volumes.

Options for Data Protection

Tivoli Storage Manager provides a variety of backup and archive operations, allowing you to select the right protection for the situation. Table 1 shows some examples of the protection options.

Table 1. Examples of Meeting Your Goals with Tivoli Storage Manager

For this goal... Do this...
Back up files that are on a user's workstation, and have the ability to restore individual files. Use the backup-archive client to perform incremental backups or selective backups.
Back up a file server, and have the ability to restore individual files. Use the backup-archive client to perform incremental backups or selective backups.

If the file server is a network-attached storage file server that is supported, you can use Tivoli Data Protection for NDMP to perform image backups.

Make restore media portable, or make restores easier to perform remotely. Use the backup-archive client to perform incremental backups, and then generate backup sets by using the Tivoli Storage Manager server.
Provide the ability to more easily restore the entire contents of a single logical volume, instead of restoring individual files. Use the backup-archive client to perform logical volume backups (also called image backups).
Set up records retention to meet legal or other long-term storage needs. Use the backup-archive client to occasionally perform archiving. To ensure that the archiving occurs at the required intervals, use central scheduling.
Create an archive for a backup-archive client, from data that is already stored for backup. Use the backup-archive client to perform incremental backups, and then generate a backup set by using the Tivoli Storage Manager server. This is also called instant archive.
Provide the ability to restore data to a point in time. Use the backup-archive client to regularly perform incremental backups (either manually or automatically through schedules). Then do one of the following:
Save a set of files and directories before making significant changes to them. Use the backup-archive client to archive the set of files and directories.

If this kind of protection is needed regularly, consider creating backup sets from backup data already stored for the client. Using backup sets instead of frequent archive operations can reduce the amount of metadata that must be stored in the server's database.

Back up data for an application that runs continuously, such as a database application (for example, DB2(R) or Oracle) or a mail application (Lotus(R) Domino(TM)). Use the appropriate application client. For example, use Tivoli Data Protection for Lotus Domino.
Exploit disk hardware capable of data snapshots. Use the appropriate component that supports the hardware, such as Tivoli Data Protection for IBM Enterprise Storage Server(TM).
Make backups transparent to end users. Use the backup-archive client with centrally scheduled backups that run during off-shift hours. Monitor the schedule results.
Reduce the load on the LAN by moving backup data over your SAN.

Use LAN-free data movement or, for supported network-attached storage (NAS) file servers, use Tivoli Data Protection for NDMP.

Schedule the backups of client data to help enforce the data management policy that you establish. If you schedule the backups, rather than rely on the clients to perform the backups, the policy that you establish is followed more consistently. See Chapter 14, Scheduling Operations for Client Nodes.

The standard backup method that Tivoli Storage Manager uses is called progressive incremental backup. It is a unique and efficient method for backup. See Progressive Incremental Backup Compared with Other Backup Types.

Table 2 summarizes the client operations that are available. In all cases, the server tracks the location of the backup data in its database. Policy that you set determines how the backup data is managed.

Table 2. Summary of Client Operations

Type of operation Description Usage Restore options For more information
Progressive incremental backup The standard method of backup used by Tivoli Storage Manager. After the first, full backup of a client system, incremental backups are done. Incremental backup by date is also available.

No additional full backups of a client are required after the first backup.

Helps ensure complete, effective, policy-based backup of data. Eliminates the need to retransmit backup data that has not been changed during successive backup operations. The user can restore just the version of the file that is needed.

Tivoli Storage Manager does not need to restore a base file followed by incremental backups. This means reduced time and fewer tape mounts, as well as less data transmitted over the network.

See Incremental Backup and Backup-Archive Installation and User's Guide.
Selective backup Backup of files that are selected by the user, regardless of whether the files have changed since the last backup. Allows users to protect a subset of their data independent of the normal incremental backup process. The user can restore just the version of the file that is needed.

Tivoli Storage Manager does not need to restore a base file followed by incremental backups. This means reduced time and fewer tape mounts, as well as less data transmitted over the network.

See Selective Backup and Backup-Archive Installation and User's Guide.
Adaptive subfile backup A backup method that backs up only the parts of a file that have changed since the last backup. The server stores the base file (the complete initial backup of the file) and subsequent subfiles (the changed parts) that depend on the base file.

The process works with either the standard progressive incremental backup or with selective backup.

Applicable to clients on Windows(R) systems.

Maintains backups of data while minimizing connect time and data transmission for the backup of mobile and remote users. The base file plus a maximum of one subfile is restored to the client. See Enabling Clients to Use Subfile Backup and Backup-Archive Installation and User's Guide.
Journal-based backup Aids all types of backups (progressive incremental backup, selective backup, adaptive subfile backup) by basing the backups on a list of changed files. The list is maintained on the client by the journal engine service of Tivoli Storage Manager. Reduces the amount of time required for backup. The files eligible for backup are known before the backup operation begins.

Applicable to clients on Windows NT(R) and Windows 2000 systems.

Journal-based backup has no effect on how files are restored; this depends on the type of backup performed. See Backup-Archive Installation and User's Guide.
Image backup Full volume backup.

Nondisruptive, on-line backup is possible for Windows 2000 clients by using the Tivoli Storage Manager snapshot function.

Allows backup of an entire file system or raw volume as a single object. Can be selected by backup-archive clients on UNIX(R) and Windows systems. The entire image is restored. See Policy for Logical Volume Backups and Backup-Archive Installation and User's Guide.
Image backup with differential backups Full volume backup, which can be followed by subsequent differential backups. Used only for the image backups of NAS file servers, performed by using Tivoli Data Protection for NDMP. The full image backup plus a maximum of one differential backup are restored. See Chapter 6, Setting Up Tivoli Data Protection for NDMP.
Backup using hardware snapshot capabilities A method of backup that exploits the capabilities of IBM Enterprise Storage Server FlashCopy(TM) and EMC TimeFinder to make copies of volumes used by database servers. The Tivoli Data Protection for applications and databases then uses the volume copies to back up the database volumes. Implements high-efficiency backup and recovery of business-critical applications while virtually eliminating backup-related downtime or user disruption on the database server. See the referenced publications for details. See Tivoli Data Protection for IBM ESS for Oracle Databases DB2 UDB Installation and User's Guide, Tivoli Data Protection for IBM ESS for R/3 Installation and User's Guide, and Tivoli Data Protection for EMC Symmetrix for R/3 Installation and User's Guide.
Archive The process creates a copy of files and stores them for a specific time. Use for maintaining copies of vital records for legal or historical purposes.
Note:
If you need to frequently create archives for the same data, consider using instant archive (backup sets) instead. Frequent archive operations can create a large amount of metadata in the server database resulting in increased database growth and decreased performance for server operations such as expiration. Frequently, you can achieve the same objectives with incremental backup or backup sets. Although the archive function is a powerful way to store inactive data with fixed retention, it should not be used on a frequent and large scale basis as the primary backup method.
The selected version of the file is retrieved on request. See Archive and Backup-Archive Installation and User's Guide.
Instant archive The process creates a backup set of the most recent versions of the files for the client, using files already in server storage from earlier backup operations. Use when portability of the recovery media or rapid recovery of a backup-archive client is important. Also use for efficient archiving. The files are restored directly from the backup set. The backup set resides on media that can be mounted on the client system, such as a CD, a tape drive, or a file system. The Tivoli Storage Manager server does not have to be contacted for the restore process, so the process does not use the network or the server. See Creating and Using Client Backup Sets.

Progressive Incremental Backup Compared with Other Backup Types

Tivoli Storage Manager has a unique, efficient method for its standard backups, as well as a number of other methods that are summarized in Table 2. The standard method that Tivoli Storage Manager uses is progressive incremental backup.

The terms differential and incremental are often used to describe backups. The terms usually have the following meanings:

Tivoli Storage Manager takes incremental backup one step further. After the initial full backup of a client, no additional full backups are necessary because the server, using its database, keeps track of whether files need to be backed up. Only files that change are backed up, and then entire files are backed up, so that the server does not need to reference base versions of the files. This means savings in resources, including the network and storage.

If you choose, you can force full backup by using the selective backup function of a client in addition to the incremental backup function. You can also choose to use adaptive subfile backup, in which the server stores the base file (the complete initial backup of the file) and subsequent subfiles (the changed parts) that depend on the base file.

Additional Protection: Storage Pool and Server Database Backups

Built into the server are additional levels of protection for client data:

These backups can become part of a disaster recovery plan, created automatically by Tivoli Disaster Recovery Manager. See Chapter 23, Using Tivoli Disaster Recovery Manager.

How Data Moves to Server Storage

The Tivoli Storage Manager client traditionally sends its data to the server over the LAN. The server then transfers the data to a device that is attached to the server. With the advent of SAN and network-attached storage, however, Tivoli Storage Manager offers options that enable you to minimize use of the LAN and the use of the computing resources of both the client and the server.

LAN-free data movement allows storage agents that are installed on client nodes to move data without sending the data over the LAN to the server. See LAN-Free Data Movement.

For network-attached storage, use Tivoli Data Protection for NDMP to avoid data movement over the LAN. See Tivoli Data Protection for NDMP Backups.

Consolidating Backed-up Data for Clients

By grouping the backed-up data for a client, you can minimize the number of media mounts required for client recovery. The server offers you methods for doing this:

Collocation
The server can keep each client's files on a minimal number of volumes within a storage pool. Because client files are consolidated, restoring collocated files requires fewer media mounts. However, backing up files from different clients requires more mounts.

You can have the server collocate client data when the data is initially stored in server storage. If you have a storage hierarchy, you can also have the data collocated when the server migrates the data from the initial storage pool to the next storage pool in the storage hierarchy.

Another choice you have is the level of collocation. You can collocate by client or by file space per client. Your selection depends on the size of the file spaces being stored and the restore requirements.

See Keeping a Client's Files Together: Collocation.

Backup set creation
You can generate a backup set for each backup-archive client. A backup set contains all active backed-up files that currently exist for that client in server storage. The process is also called instant archive.

The backup set is portable and is retained for the time that you specify. Creation of the backup set consumes more media because it is a copy in addition to the backups that are already stored.

See Creating and Using Client Backup Sets.

Moving data for a client node
You can consolidate data for a client node by moving the data within server storage. You can move it to a different storage pool, or to other volumes in the same storage pool.

See Moving Data by Node.


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