Turning on the "larger than 16GB" feature of Exchange 2003 SP2
I learned an interesting tidbit of information from John Savill's Windows Tips & Tricks FAQ (www.windowsitpro.com). The feature of Exchange 2003 Service Pack 2 that allows a database to be larger than 16GB is NOT enabled by default. There is a Registry value that you need to create to define the maximum database size. In my example, the server name is HNLEX01. Locate the following registry key in HKLM\SYSTEM\CurrentControlSet\Services
The value of GUID is a unique identifier for that particular database and will be different for each installation. For Exchange 2003 Standard Edition, there will only "Private" GUID, though.
Create a REG_DWORD value called Database Size Limit in GB. Set the new value to a value between 1 and 75GB. Remember that the default entry field for REG_DWORD values is hexadecimal, so remember to click the Decimal radio button. If this key does not exist, then the default database size will remain at 16GB.
There is another registry value that you can create that defines a warning level above which the an event will be logged if the database exceeds a remaining percentage of its maximum size. In the same registry key as above, create a REG_DWORD value called Database Size Buffer in Percentage and set it to between 1 and 100 percent. (Once again, remember the default for this interface is hexadecimal, so remember to click the Decimal radio button.) The default is 10, which means when the database has only 10% of its available size left, you will start seeing warnings in the event viewer. These warnings are generated at 5:00AM, by defaut, but you can define a registry value (in the same key as the two above values) that defines an offset from midnight at which a warning limit is generated. Create a REG_DWORD value called Database Size Check Start Time In Hours From Midnight and set it to a value from 1 to 23 (in decimal). While John Savill's FAQ did not say whether or not the store needs to be dismounted and remounted for this to take effect, I'm betting it does.
Remember that Exchange 2003 Service Pack 2 is still in beta and should NOT be installed in production. I am not sure in the final release of Exchange 2003 SP2, if the database size will automatically be extended to 75GB of if you will have to do this via registry.
If your Exchange 2003 Standard Edition database has exceeded 16GB and Service Pack 2 is not yet available, you can temporarily extend the size of the database by 1GB. See Microsoft KG article 813051: How to temporarily increase the Exchange 2000 16-gigabyte database size limit.