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title: "Disaster Recovery - Introduction"
canonical: "https://kb.myframeworks.com.au/space/PROSTIXV48DOC/31097534/Disaster%20Recovery%20-%20Introduction"
format: markdown
---
Introduction   The backbone of the Sterland Disaster Recovery module lies in the Progress After Imaging (AI) function, and the Open Source utility 'rsync' that provides fast incremental file transfer between systems. With Progress AI, changes to the production database are also written to additional AI files (which are also referred to as the redo-logs).  The prime function of after imaging allows changes made to the database to be stored on separate physical disks, so that in the event of total disk failure where the database resides, the database can be restored and the AI logs re-applied up to the point just before the failure. It also allows recovery from accidental human error, where data that was deleted can be recovered from the AI logs. In a Disaster Recovery (DR) situation where a separate DR backup server is maintained, an entire copy of the Production database, referred to as the Warm Spare database, can be kept in sync with the production database. This is achieved by applying, or rolling forward to use the Progress terminology, the AI logs taken from the production database. With the rsync utility, individual files or entire directory structures can easily be kept in s ync on a secondary system, where only the incremental changes are copied over the network. This provides a very efficient method of keeping all of the other application and some of the operating system files in sync on the DR server. This User Guide outlines the steps & tasks involved in monitoring, testing, switching & recovering between the Production and DR servers.