Hello,
From the docs here...
Best Practices for Managing Subscriber Mailbox Size
You can manage subscriber mailbox size in the following ways:
Understand How Cisco Unity Handles Full Mailboxes and How Performance Is Affected by Mailbox Size
To learn more about how Cisco Unity handles subscribers with full mailboxes, refer to the "How Cisco Unity Handles Full Mailboxes" section in the "About Message Handling" section in the "Messaging and Default Accounts Overview" chapter of the System Administration Guide for Cisco Unity. (The guide is available at http://cisco.com/en/US/products/sw/voicesw/ps2237/prod_maintenance_guides_list.html.)
Because the processing of messages happens in real-time when the users log on to check their messages, mailbox size directly affects Cisco Unity conversation performance. For mailbox size recommendations and other performance considerations, see the "Administrative Monitoring Guidelines for Cisco Unity Performance" section on page 6-8.
Understand That Codec Choice Affects Message File Size
As illustrated in Table 2-3, the codec used to record a voice message has an effect on the file size of the message. Messages recorded with the G.711 Mu-Law and A-Law codec require the most disk space to store, while the G.729a codec offers the smallest file size.
Stored voice messages can consume considerable amounts of disk space. The amount of storage a WAV file uses depends on what kind of compression the codec uses, if any. The higher the compression, the smaller the file and the affect on the disk-space of the database and at the subscriber workstation. However, some sound-quality reduction and some CPU processing overhead may result when compressing messages during recording and decompressing at playback.
Note
Audio quality ratings are subjective, and are provided here only for basic comparison between the different fully supported codecs.
To change the audio code that Cisco Unity uses for recording voice messages, use the Set Record Format Tool in Tools Depot. (To open Tools Depot, on the Cisco Unity server desktop, double-click the Cisco Unity Tools Depot icon.)
