Using NetBackup for SQL Server with Snapshot Client How SQL Server operations use Snapshot Client
then a point in time recovery could be achieved by restoring the full database from Tuesday at 12AM, followed by the differential at 6PM on Tuesday, and finally the transaction log at 8PM (specifying “TO 7:50 PM”).
However, in some situations with persistent frozen image backups, it may not be feasible to retain the daily full backup after the next full backup has been created. So, if a point in time restore is required prior to the latest backup, the differentials would effectively be based on backups that no longer exist. Thus the only alternative would be to recover based upon the last full backup that had been retained using a potentially long sequence of transaction log images.
To resolve this issue, NetBackup allows you to create SQL Server Snapshot Client backups that are not recorded in the MSDB. To create these backups in SQL Server 2005, NetBackup uses the copy-only backup feature, which allows the backups to be created as out-of-band. In SQL Server 2000, since copy-only backups are not available, NetBackup allows these backups to be cloaked, effectively creating the backup without telling SQL Server.
In SQL Server 2000, NetBackup uses cloaking to provide SQL Server with an “unsuccessful” status thereby inhibiting SQL Server from recording that the backup had occurred. Due to the unsuccessful status, the job line of the MSSQL progress monitor will show a -1 status, whereas the NetBackup server job monitor registers the job as successful. NetBackup places information in its catalog to denote when a backup has been cloaked and uses this information in determining full database recovery paths. In SQL Server 2005, cloaking is not needed because SQL Server does not record the backup, but simply declares it as copy-only.
Sample backup schedule using cloaked backups
To understand how recovery staging works with copy-only or cloaked backups, consider a sample backup schedule with the following characteristics:
The transaction log is backed up frequently, e.g., every two hours
A full backup is saved to secondary storage, such as tape, once every several days
Differential database backups are created several times per day
A persistent frozen image backup is created several times per day and expires when the next one is created. This backup is created as copy-only (SQL Server 2005) or it is cloaked (SQL Server 2000).