Online Backup

Online Backup

InterSystems IRIS implements a proprietary backup mechanism designed to cause very minimal or no downtime to users of the production system. Online backup, which only backs up data in IRIS.DAT files, captures all blocks in the databases that are allocated for data. The output goes to a sequential file. This must be coordinated with a system backup to copy the online backup output file to the backup media along with other files. This system backup must include all file systems in use by the system, excluding IRIS.DAT files. At a minimum it must include the installation directory, journal and alternate journal directories, Web Gateway files, and any directory containing external files used by InterSystems IRIS. Do not include IRIS.DAT files.

The online backup procedure uses multiple passes to copy data, where each consecutive pass copies an incrementally reduced list of data blocks that changed during the previous pass. Generally, three passes are sufficient to complete a backup. During the entire final pass and for a brief moment during each prior pass, the process pauses writes to the database. The backup pauses physical writes to the database while allowing user processes to continue performing updates in memory.

Given the capabilities of today’s external backup options, it is usually possible to find an external backup approach that suits your needs better than online backup. The following table lists the advantages and disadvantages of the online backup strategy:

There are different types of online backup, which you can combine to manage the trade-offs between the size of the backup output and the time needed to recover from the backup:

• Full Backup — Writes an image of all in-use blocks to the backup media.

• Cumulative Backup — Writes all blocks that have been modified since the last full backup. Must be used in conjunction with a previous full backup.

• Incremental Backup — Writes all blocks that have been modified since the last backup of any type. Must be used in conjunction with a previous full backup and (optionally) subsequent cumulative or incremental backups.

When using online backup, you must first run a full backup, after which you can run cumulative and/or incremental backups.

Online backup writes all database blocks to a single file in an interleaved fashion. When you back up an extremely large amount of data using the online backup, restores can become somewhat cumbersome; consider this when planning your backup strategy.

The restore validation process helps resolve any limitations by providing an online, restored copy of the databases. Use the same backup validation strategy when running incremental or cumulative backups. After you perform each incremental or cumulative backup, you can immediately restore to the alternate server. For example, a strategy of weekly full backups and daily incremental backups can work well because each daily backup contains only the blocks modified that day. Using this strategy, you should restore the incremental backup to the alternate server each day, and check the integrity of the restored databases.

Avoid overwriting the warm copy of the last known good backup when restoring the backup you are currently validating. The same concept applies when restoring an incremental to the existing restored database. After you establish that the backup is the last known good backup and before applying the next day’s incremental or cumulative backup to it, save a copy so that the last known good backup is always online and ready for use in case the subsequent incremental restore fails. If a restored backup fails an integrity check, you must discard it; you cannot use it as a target of a subsequent incremental restore.

When restoring a system from an online backup, first restore the most recent full backup, followed by the most recent cumulative backup, and then all incremental backups taken since the cumulative backup.

For information about configuring online backup, see Configuring Online Backup Settings; for information about performing online backups, see Managing Online Backups.