ASA Database Administration Guide
Backup and Data Recovery
Configuring your database for data protection
Both a live backup and a transaction log mirror appear to provide a secondary copy of the transaction log. However, there are several differences between using a live backup and using a transaction log mirror:
In general, a live backup is made to a different machine Running a transaction log mirror on a separate machine is not recommended. It can lead to performance and data corruption problems, and stops the database server if the connection between the machines goes down.
By running the Backup utility on a separate machine, the database server does not do the writing of the backed up log file, and the data transfer is done by the Adaptive Server Anywhere client/server communications system. Therefore, performance impact is decreased and reliability is greater.
A live backup provides protection against a machine becoming unusable Even if a transaction log mirror is kept on a separate device, it does not provide immediate recovery if the whole machine becomes unusable. You could consider an arrangement where two machines share access to a set of disks.
A live backup may lag behind the database server A mirrored transaction log contains all the information required for complete recovery of committed transactions. Depending on the load that the server is processing, the live backup may lag behind and may not contain all the committed transactions.
The live backup of the transaction log is always the same length or shorter than the active transaction log. When a live backup is running, and another backup restarts the transaction log (dbbackup -r or dbbackup -x), the live backup automatically truncates the live backup log and restarts the live backup at the beginning of the new transaction log.
For more information about how to make a live backup, see Making a live backup.