If you need to back up specific databases, you can do that by creating a user-defined subclient.
Procedure
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From the navigation pane, go to Protect > Exchange.
The Exchange page appears.
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Click an Exchange database.
The Exchange Database page appears.
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Click Add Subclient.
The Add subclient wizard appears.
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On the General page, type a name for the subclient, select a plan, and then click Next.
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On the Settings page, type or select the maximum number of streams that is required for running a backup operation.
By default, the number of streams is 2.
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Optional: If you want block-level backup operations to use the backed-up databases for live browse, select the Optimize for message level recovery check box.
You can also enable block-level backups later. For more information, see Enabling Block-Level Backups for Exchange Databases.
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Click Next.
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On the Subclient content page, select the databases that you want to add to the user-defined subclient, and then click Next.
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On the Server details page, specify whether to select the backup source manually or automatically:
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To manually select the backup source, select Manual selection, and then, for each database, select the server that you want to use as the backup source.
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To have the software automatically select the backup source, complete the following steps:
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Select Automatic selection.
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To use a passive server, select the Backup from passive copy check box.
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To use the active server when no passive server is available, select the Backup from active copy if no passive copy is available check box.
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To run backup operations on the server that is least likely to become active in a failover case, select the Use last activation preference to select passive copy check box.
For more information, see Configuring Manual or Automatic Selection of the Backup Source.
 
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Click Save.
 
Result
The user-defined subclient appears on the Exchange Database page, under Subclients.