Both a live backup and a transaction log mirror 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 computer By running the Backup utility on a separate computer, the database server does not do the writing of the backed up log file, and the data transfer is done by the SQL Anywhere client/server communications system. Therefore, performance impact is decreased and reliability is greater.
Running a transaction log mirror on a separate computer is not recommended. It can lead to performance and data corruption problems, and stops the database server if the connection between the computers goes down.
A live backup provides protection against a computer becoming unusable Even if a transaction log mirror is kept on a separate device, it does not provide immediate recovery if the whole computer becomes unusable. You could consider an arrangement where two computers 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. See Making a live backup.