Hi Krishna,
I have not tried this setup but it is supported. My take on this is that the BARS Utility would have to be uninstalled and then reinstalled with the Sub named as the Backup Server and the Pub as the Backup Target. I might look at what is consuming so much disc space though before I went this route. Perhaps the drive is filling up with Trace Files that need to be turned of or CDR Records that are not being purged.
About the Backup Server
Although any server in the Cisco CallManager cluster can act as the backup server, Cisco recommends that you designate the publisher database server as the backup server, which is the server that performs the backup. One backup server is required within a Cisco CallManager cluster. You designate a server as a backup server during BARS installation.
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Note The Cisco CallManager publisher database contains all the information that you configure with Cisco CallManager Administration, and the database updates each time that you make a change. Cisco strongly recommends that you make a backup of the Cisco CallManager database, configuration, and directory information by using BARS every time that you make changes in Cisco CallManager Administration. Each Cisco CallManager cluster contains only one publisher database.
The following list shows the data that is backed up and restored for the Cisco CallManager publisher database:
Hosts and LMhosts files
Latest Cisco CallManager publisher database
DC Directory LDAP directory
For Cisco CallManager 3.3.x DirectoryConfiguration.ini from C:\dcdsrvr.
For Cisco CallManager 4.0(x) or later UMDirectoryConfiguration.ini.
Directory schema files avvid_schemaV*.txt
Publisher and subscriber configuration information to replication.ini file.
Cisco CallManager version to version.ini file.
If the option to backup CDR is chosen, CDR database and CDR/CMR flat files from Local CDR Path
TFTP files from C:\Program Files\Cisco\TFTPPath (the default path)
TFTP files from alternate file locations
Cisco Bulk Administration Tool (BAT) files-templates from C:\CiscoWebs\BAT, CSV files from C:\BAT and the BATversion.asp file.
HKLM\Software\Cisco Systems, Inc. (registry keys)
Cisco CallManager DSN
Security files (certificates) from under C:\Program Files\Cisco\Certificates. This applies only to Cisco CallManager 4.x or later.
LDAPConfig.ini for IPMA configuration.
From this good doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a00805e6496.html#wp43860
Hope this helps!
Rob
