System Level Backup usage considerations

Before configuring IMS Recovery Expert, it is important to consider and understand how the System Level Backups (SLB) will be used in recovery situations.

Your first consideration when planning for System Level Backup and recovery is to decide what you want to recover. For example, you can recover an entire IMS environment, you can recover just an application or database, or you can recover at a remote site. You may decide you need to do only a partial backup of an IMS system, or a data only backup. Once you determine what you want to recover, you will create a backup profile that will be tailored to your specific recovery needs.

System Level Backup (SLB) used for local system recovery

Local system recovery is the process of restoring an entire IMS environment (Full). This includes database data, logs, RECONS, and system data sets, to the point in time of a System Level Backup. Local system recovery can also include running forward recovery processes to apply changes that occurred after the System Level Backup was created. It is also possible to restore only the volumes that contain database data from a System Level Backup, and then run forward recovery processes to bring the databases to a more current state.

When IMS Recovery Expert restores an entire IMS environment, it is important to understand that it does the restore at a volume level. When a volume is restored, it will restore all data sets that were on the volume at the time of the System Level Backup, and it will overlay changes or new data sets that were created on the volumes since the System Level Backup. Because of this, if local system level recovery is a viable recovery scenario, it is important to analyze data set isolation (see Analyzing data set isolation) before creating any backups. This ensures that a volume level restore will yield the wanted results.

Things to check for are:

Are there non-IMS data sets on the volumes being backed up and restored? If so, is it wanted that they are restored to the same point in time as the System Level Backup?
If forward recovery is wanted after restoring the database data only, then the volumes where any archive logs, RECONs, or IMS system data sets reside must be segregated from the volumes that contain database data.
If forward recovery is wanted after restoring an entire IMS environment to the time of a System Level Backup, then the RECONs and archive logs should not be on volumes contained in the System Level Backup.
The MVS user catalogs where the data sets being backed up are cataloged must reside on the volumes being backed up. If database data and log segregation is required for the chosen recovery option, then the segregation also applies to the MVS user catalogs where the database data and log data sets are cataloged.

System Level Backup (SLB) used for application or database level recovery

Once a System Level Backup is created and the option to Enable DB Restore is enabled in the backup profile, then IMS Recovery Expert can be used to restore an entire application (group of databases and indexes) or individual databases or indexes from the System Level Backup. When IMS Recovery Expert restores at the application or database level, it does so at a data set level. After restoring the database data sets from a System Level Backup, IMS Recovery Expert can then run any forward recovery processes using the existing RECONs and archive logs.

If application or database level recovery is the only level of recovery that is needed, then data segregation is not important and IMS System Analysis and Configuration is not needed.

It is important to make sure Enable DB Restore is set to Y before creating the System Level Backup.

System Level Backup (SLB) used for remote disaster restart or disaster recovery

A System Level Backup can be created and shipped to a remote site for use in a disaster restart operation or disaster recovery operation.

Disaster restart is the process of restoring a System Level Backup at the remote site and then doing an emergency restart of IMS. IMS and the databases will be restored to the point in time when the System Level Backup was created. IMS will back out any uncommitted changes. In essence, this is the same as recovering from a power outage.

Disaster recovery operations start with the process of restoring a System Level Backup at the remote site. Then, the forward recovery processes can also be run to apply changes that occurred after the System Level Backup was created.

In either scenario, it is not important that IMS recovery structures (RECONs and logs) be segregated from the database data sets. However, it is important to verify the following by doing the IMS System Analysis and Configuration:

Non-IMS data sets might reside on the volumes included in the System Level Backup. Since the processes at the remote site will restore these volumes, ensure that you want these data sets to be restored to the point in time the System Level Backup was created.
The MVS user catalogs where the data sets for the IMS environment are cataloged must be on the volumes that are included in the System Level Backup.

See Analyzing data set isolation for more information.

Partial System Level Backup (PSLB) for database or application recovery

IMS Recovery Expert provides the capability to create a partial System Level Backup, or PSLB. A PSLB is a backup that does not include all of the volumes where an IMS system resides. A PSLB can be used for large databases or applications having unique backup requirements. Using a partial System Level Backup versus a full System Level Backup will also reduce disk utilization and allow for additional backup generations.

A PSLB can be used for database or application recovery only. A PSLB cannot be used for system recovery. Using a PSLB for database or application recovery, the data is restored at the data set level so log and database data isolation is not required. The wanted application database data should be grouped on volumes as a best practice.

Combined System Level Backup (CSLB)

The Combined System Level Backup feature can be used to include multiple IMS subsystems in a single backup. These IMS subsystems do not have to be in the same data sharing group. This backup can then be used for local system recovery, local application recovery, or disaster recovery. The Combined System Level Backup feature can also include Db2® subsystems when IMS Recovery Expert is paired with Db2 Recovery Expert. For more information about using the Combined System Level Backup feature, see Performing a Combined System Level Backup.