Remote Backup Systems
Remote backup systems provide a wide range of availability, allowing the transaction processing to continue even if the primary site is destroyed by a fire, flood or earthquake.
Data and log records from a primary site are continuously backed up into a remote backup site.
One can achieve ‘wide range availability’ of data by performing transaction processing at one site, called the ‘primary site’, and having a ‘remote backup’ site where all the data from the primary site are duplicated.
The remote site is also called ‘secondary site’.
The remote site must be synchronized with the primary site, as updates are performed at the primary.
In designing a remote backup system, the following points are important.
a) Detection of failure: It is important for the remote backup system to detect when the primary has failed.
b) Transfer of control: When the primary site fails, the backup site takes over the processing and becomes the new primary site.
c) Time to recover: If the log at the remote backup becomes large, recovery will take a long time.
d) Time to commit: To ensure that the updates of a committed transaction are durable, a transaction should not be announced committed until its log records have reached the backup site.
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