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Using NetBackup for SQL Server with Snapshot Client How SQL Server operations use Snapshot Client

Selection of backup method

The selection of a backup methodology, whether standard or Snapshot Client, is dependent on what policy is used. If a policy configured for Snapshot Client is selected, then additional attributes relating to the policy determine the Snapshot Client features and specific snapshot methods used.

Limitations

Due to SQL Server limitations certain objects cannot be backed up via snapshots. These are database differentials, filegroup differentials, and transaction logs. If an Snapshot Client policy is selected to back up one of these object types, then NetBackup will perform a stream-based backup using the storage unit provided in the policy configuration. If a storage unit is not provided, then NetBackup will use the default storage unit for the server.

What is backed up

Although the database administrator works exclusively with logical objects, such as databases and filegroups, it is useful to gain some appreciation of the differences between file- and stream-based backups in terms of the data content that is archived. For stream-based backups, NetBackup simply captures the data stream content provided by SQL Server. If the user has specified multiple streams, then SQL Server opens multiple streams that NetBackup catalogs as separate images.

For file-based backups, NetBackup creates a file list consisting of all the physical files that constitute the object and supplies it to the Snapshot Client, which is responsible for snapshot creation. If multiple streams have been specified, then NetBackup divides the file list into sub-lists. Each sub-list is backed up separately and constitutes a separate image. Users may notice that if multiple streams are specified for a file-based backup and if the number of streams exceeds the number of component files, then the number of file-based streams will not exceed the number of files. With stream-based SQL Server backups, SQL Server always creates exactly the number of streams that the end user specifies.

The file list used for backing up a SQL Server database consists of the physical files constituting the primary filegroup, any secondary filegroups, and the transaction log. Typically, these can be identified respectively by their name extensions, which are .mdf, .ndf, and .ldf. The file list for a filegroup backup consists of the physical files belonging to the filegroup. And, finally, the file list for a SQL Server file object backup consists of a single physical file, namely, the file that maps to the SQL Server file object.

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