Concurrent External Backup

Concurrent External Backup

The concurrent external backup strategy (also known as “dirty backup”) can be used when a zero-downtime backup is needed but deployment circumstances preclude standard zero-downtime external backup or zero-downtime online backup. A typical scenario under which this strategy might be considered, for example, is when snapshot technology is not available and the databases are so large that both of the following are true:

• Using external backup, writes would be frozen (while the databases were being copied) long enough to impact users.

• Using online backup would be impractical.

The concurrent external backup strategy works by allowing an external system backup to run while normal databases writes are taking place. The copies of the databases obtained in this manner are expected to be corrupt (“dirty”). This copy is then followed by an Incremental Online Backup, which captures any database blocks that were modified while the copy took place. When restoring the backup, first the copy of the databases are restored, then the incremental backup is restored. The steps in detail are as follows:

1. Clear the list of database blocks modified since the last backup:

    Do CLRINC^DBACK("QUIET")

   

   For information, see CLRINC^DBACK.

2. Copy the IRIS.DAT database files, using your chosen operating system or third-party backup utility.

3. Call $$BACKUP^DBACK with the E parameter to indicate you used an external backup utility; for example:

    Set x=$$BACKUP^DBACK("","E","Dirty external backup - incrementals must be applied.","","","")

   

   For information, see BACKUP^DBACK.

4. Perform an incremental backup, which copies any blocks that changed while the IRIS.DAT files were being copied; this may cause a very brief suspension of user processes in some configurations:

    Set x=$$BACKUP^DBACK("","I","Nightly","test.bck","N","bck.log","QUIET","N","Y")
   

   

   For information, see BACKUP^DBACK.

5. Restore the backup according to the instructions under Full System Restore from Online Backup or Concurrent External Backup in Full System Restore.

The following table lists the advantages and disadvantages of the concurrent external backup strategy: