The MaxBack VSS Writer is a VSS Writer for MaxDb databases.
What is a VSS Writer?¶
VSS (Volume Shadow Copy Service) is a windows feature used to create consistent backups. VSS defines a backup workflow triggered by a VSS requestor (the backup tool). The VSS Writers are part of this workflow and responsible for setting a application in a consistent state before backup and after restore.
- A detailed explanation of the VSS service can be found in the wikipedia:
How it works¶
The VSS workflow always executes the following steps on a VSS Writer during a Backup:
- Prepare Backup event
At this event the MaxBack VSS writer analyze the database state and verifies if the backup includes the database files. If the database files are included in the backup, the writer requests to participate in the backup.
- Prepare Snapshot event
If enabled the VSS Writer will now execute the log file backup to include it in the snapshot. The database will now be checked if it is online. If this is the case it is set into consistent state using the external backup feature of MaxDb.
The external backup function is available since MaxDb 7.8.2. See SAP note https://launchpad.support.sap.com/#/notes/1928060 for details.
- Freeze event
On freeze the VSS Writer writes information to the file system that is used to detect a bare metal / or Virtual Machine Recovery. As the database is allready in consistent state nothing is changed on it.
- Snapshot creation
The VSS service will now create a snapshot of the volumes saved in the backup.
- Thawn event
The VSS writer removes the information to detect bare metal / or Virtual Machine Recovery information.
- Post snapshot event
Not used by the Maxback VSS Writer
- Backup completed event
When the backup is completed sucessfully the VSS services notifies the VSS Writers about the backup state.
It everything has been backed up, the running backup will be confirmed and written to the MaxDb backup history. Additionally logs will be truncated (if enabled) and the logs created during the backup operation will be written to the file system.