Part of my role is to understand trends and determine how technically we can solve our supportability issues. While performing some reviews of cases related to store startup, I was shocked at the number of cases where the 16GB limit of the standard version of Exchange was reached. For the standard version of Exchange you are limited to a single mailbox and public folder database with a maximum size of 16gb. One can argue that it’s an archaic limit, but I’ll leave the final decision up to the marketing guys on how we treat this in future products.
For those of you out there running the standard edition, you have an additional task and that is to monitor the size of the priv and pub EDB files. Once you reach this limit the store will be dismounted. The KB article below explains how you can extend the limit by 1gb, but remember this isn’t a permanent solution. Offline defrag and other steps should be taken immediately to prevent the database from continuing to dismount unexpectedly.
Refer to this article for more details on the 16gb limit scenario: http://support.microsoft.com/?id=828070
Along these same lines the other major issue observed was disk full scenario. This is true for both Standard and Enterprise editions. In many of the cases drive(s) would simply fill up with transaction logs, database growth, or large amounts of data being stored on the same drive as the databases/logs. When this occurs, the database goes down hard, typically requiring drastic measures to get the database operational again.
I thought this was just worth mentioning considering these two issues accounted for the largest majority of issues where the stores would not mount and are both easily managed, but yet require the greatest amount of time for recovery.