• The database size limit registry keys are read when the database mounts (not when the service starts up), and when each limit check task runs.
  

You must set registry parameters for each database targeted for size limit modification. The registry entries should be located under each database entry in the local server registry. Accordingly, you must reset the registry keys manually if the server has to be rebuilt using the /disasterecovery setup switch.

Note:
Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data.

All registry settings discussed in this topic are created in the following registry location:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\<SERVER NAME>\Private-013e2e46-2cd7-4a8e-bfec-0e4652b94b00

The GUID in this key (Private-013e2e46-2cd7-4a8e-bfec-0e4652b94b00) is an example and should match the value of the objectGUID attribute on the database’s Active Directory object.

Note:
By default, registry entries mentioned in this article are not present; when you create the entry, you override the default value set in code.

Note:
All of registry values mentioned in this article are in decimal, not hexadecimal.

• The following new registry settings are available with SP2:
  
• Database Size Limit in GB
  
• Database Size Buffer Warning in Percentage
  
• Database Size Check Start Time in Hours from Midnight
  

The Database Size Limit in GB setting is the configurable maximum size of a database not to exceed the maximum licensed size of your database. For Standard Edition, you can set the database size limit between 1 and 75 GB. By default, the limit is 18 GB. For Enterprise Edition you can set the database size limit between 1 and 8,000 GB. By default, there is no limit.

The following registry value controls the Configurable Database Size Limit:

The Database Size Buffering in Percentage setting is a configurable error threshold that will warn you with an event log entry when your database is at or near capacity, and will shut down within 24 hours of the event being logged. By default, Exchange Server 2003 SP2 logs events when the database has grown to within 10 percent of the configured database size limit. This threshold is configurable. The smallest buffer is 1 percent of the configured size limit.

The following registry value controls the Database Size Buffer:

The Database Size Check Start Time in Hours from Midnight setting allows you to configure when the system will check your database to see if it is over the currently configured Database Size Limit. By default, the database size check happens at 05:00 (5:00 A.M.) every day. This time can be changed. If modified, the next task is scheduled at the new Offset hour. Checks at Database Size Check Interval are skipped until new start time.

First database size check will not take the database offline if the size limit has been exceeded. Because the database does not go offline, you are ensured at least 24 hour of availability after the limit is exceeded for default settings.

When a database mounts, the store process compares the physical database size against the Configured Database Size Limit in GB. If the physical size is within or exceeds the configured Database Size Warning Buffer in Percentage, the store performs a logical calculation of the database size. If it is below this warning buffer, there is no need to calculate the free space because the logical size will never exceed the physical size. Generally, the physical size is less than the warning threshold, so the size check should take under a millisecond to complete. If the free space calculation must be performed, the size check may require a few seconds to parse through the database to generate the logical size calculation.

If the Database Size Warning Buffer in Percentage is reached or exceeded, an error event, event ID 9688, is logged in the Application event log.

With Exchange Server 2003 SP2 or later, the server performs the following tasks when the configurable (or default configured) database size limit is reached:

• If the first check after a database mount finds the database size above the limit, the database will not be taken offline but an error event (ID 9689) will be logged in the Application event log.
  
• If it is the second check, an error event will be logged in the Application event log and the database will be taken offline.
  

After the administrator remounts the database, he or she has 24 hours (or until the next database size check or 05:00 if the default is set) to take corrective actions.

Exchange Server 2003 Standard Edition is limited to a single storage group with a single private information store database and a single public folder database. Prior to SP2, each database was limited to 16 GB of total physical size. SP2 increases the licensed database size limit for Exchange Server 2003 Standard Edition from 16 GB to 75 GB; the default configured database size limit will be 18 GB. Exchange Server 2003 Enterprise Edition storage group and Exchange store options do not change with the application of SP2. However, a configurable Exchange store size limit is added to the Enterprise Edition.

Note:
The current hard coded limit of the JET database is 8,192 GB, or 8 terabytes (TB).

If you change the size limit of your Exchange databases, you may want to re-evaluate your Exchange database backup and restore plan. Specifically, if you increase the size limit of the Exchange databases, be sure to test your backup and recovery operations using the new database size limits to make sure that you can still meet your service level agreements. For example, if the previous size of a mailbox store was 15 GB and you were able to meet your service level agreement by recovering the data in less than 8 hours, you may no longer be able to recover the database that quickly if you increase the size of a mailbox store to 20 GB or larger.

For information about service level agreements, see "Establishing a Service Level Agreement" in "Setting Availability Goals" in the Exchange 2003 High Availability Guide.

For information about how to configure database size limit options, see "Configure Database Size Limits" in the Exchange Server 2003 SP2 online Help.