Caché High Availability Guide - InterSystems Documentation

Importance of JournalsDepending on your needs, performance requirements of the storage device used for restoringbackups may be less stringent, perhaps allowing for a less expensive storage solution. In thisway, the last known good backup is always available for use in a disaster even if validationof the current backup fails. Retain all journal files corresponding to the last known backupuntil you identify a new backup as the last known good backup. To protect the enterprisefrom a disaster that could destroy the physical plant, regularly ship backup media to a secureoff-site location.Backups can be performed during transaction processing. In this case, the resulting backupfile contains partial transactions. When restoring from a backup, you first restore the backupfile, then restore from the journal file to complete the partial transactions in the backup file.2.2 Importance of JournalsThe backup of a Caché database alone is not enough to provide a viable restore of productiondata. In the event of a disaster that requires restoring from backup, you will always applyjournal files to the restored copy of the database. Applying journal files restores all journaledupdates from the time of the backup, up to the time of the disaster. Also applying journals isnecessary to restore the transactional integrity of your database by rolling back uncommittedtransactions (the databases may have contained partial transactions at the time of the backup).It is critical to ensure that journal files are available to be restored in the event of a disaster.Take the following steps to prevent compromising the journal files in the event of a disasterthat requires you to restore databases.• Verify that all databases for which durability and recoverability is required are set to bejournaled.• A journal file must not be purged unless it was closed prior to the last known good backup,as determined by the backup validation procedure discussed previously. Set the numberof days to keep journal files appropriately.• Define an alternate journal directory.• The primary and alternate journal directories should reside on disk devices that are separatefrom the storage of the databases, separate from the storage of the write-image journal(WIJ), and separate from each other (primary and alternate journal directories shouldreside on different devices). For practical reasons, these different devices may just bedifferent logical unit numbers (LUNs) on the same storage area network (SAN), but thegeneral rule is the more separation the better. As best as possible, the system should beCaché High Availability Guide 17