Continuous log restore

A continuous log restore keeps a second system available to replace the primary system if the primary system for restoring logs fails.

Normal log restore restores all of the available log file backups and applies the log records. After the last available log is restored and applied, the log restore finishes. Transactions that are still open are rolled back in the transaction cleanup phase, then the server is brought into quiescent mode. After the server is quiesced, no more logical logs can be restored.

With continuous log restore, instead of transaction clean up the server is put into log restore suspended state after the last available log is restored. The restore client (ontape or ON-Bar) exits and returns control to you. With the server in this state, you can start another logical restore after additional logical logs become available. As long as you start each log restore as a continuous log restore, you can continue this cycle indefinitely.

One use of continuous log restore is to keep a second system available in case the primary system fails. You can restore logical logs backed up on the primary system on the secondary system as they become available. If the primary system fails, you can restore remaining available logical logs on the secondary system and bring that secondary system online as the new primary system.

Continuous log restore requires much less network bandwidth than High-Availability Data Replication (HDR) and enterprise data replication (ER). Continuous log restore is more flexible than HDR and ER because you can start continuous log restore at any time. As a result, continuous log restore is more robust than HDR or ER in unpredictable circumstances, such as intermittent network availability.

For more information, see Configuring a continuous log restore by using ON-Bar and Configuring continuous log restore with ontape.