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Upgrading drives and adding RAID on Cisco Unity servers is not supported. They come with fixed configurations and should not be upgraded.
If you need to upgrade the server hardware and still have it supported, upgrade to a newer server.
If you do not have enough disk space on the Cisco Unity server, you can reduce the size of the database if the size has not increased too much.
To help decrease the size of the database, refer to the Message Store Manager training video.
Also, you can check the size of the MDBDATA folder.
To keep down the size of the hard drives, enable circular logging. Go to Start > Programs > Microsoft Exchange > System Manager > Servers. Right click on First Storage Group. Make sure the Enable Circular Logging box is checked.
For more information, refer to Turn Circular Logging Off.