Using the SQL Anywhere Volume Shadow Copy Service (VSS)

SQL Anywhere is compatible with the Microsoft Volume Shadow Copy Service (VSS). You can use VSS to create point-in-time snapshots of entire disk volumes or volume sets and to make copies of files that are open for exclusive use by applications such as the SQL Anywhere database server. VSS is supported on 32-bit Windows XP operating systems and on 32-bit and 64-bit editions of Windows 2003 and later operating systems, including Windows Vista.

By default, all SQL Anywhere databases can use the VSS service for backups if the SQL Anywhere VSS writer (dbvss12.exe) is running. You can use VSS without the SQL Anywhere VSS writer to back up databases. However, you might need to use the full SQL Anywhere recovery procedures to restore those databases. To prevent a database server from participating in the VSS service, include -vss- when starting the database server. Alternatively, you can use the Service utility (dbsvc) for Windows to specify when the VSS service is started.

How VSS works with SQL Anywhere:

  • Your backup application sends a command to VSS to take a snapshot.

  • VSS issues an identify command to the SQL Anywhere VSS writer (dbvss12.exe).

  • VSS issues a prepare to snapshot command to suspend all transactions and write all modified pages to disk on all databases on all database servers. If transactions are not suspended on a database within 10 seconds, the snapshot might contain uncommitted transactions and full recovery may be necessary.

  • VSS issues a freeze command to checkpoint and then suspend all activity on all databases on all database servers. Each SQL Anywhere database server waits a maximum of 60 seconds for all databases to suspend all activity. Typically, this process takes a few seconds.

  • VSS issues a thaw command to the SQL Anywhere VSS writer to resume all transactions on all databases on all database servers.

In rare circumstances, SQL Anywhere might be unable to suspend transactions or complete a checkpoint within the maximum time allowed by VSS. If this occurs, you must use the transaction log file and the full recovery process to recover the backed up database.

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