Where the hell did that 1TB limit come from?

TL;DR Exchange 2013 RTM std retains an undocumented feature from Exchange 2010; the 1TB limit on database size. This persists even after applying cumulative updates for databases created while Exchange was at RTM. The fix is to follow advice for Exchange 2010, and then move your mailboxes to a new database.


So what actually happened? Well, my customer experienced a forced dismount of a database. Digging through the event logs, there were these events:


When they tried to mount the DB, they saw this error:


Note the warning event occurred 24 hours before the error event. Also note that the size of the database really wasn’t 3.3 petabytes. As it happens, the customer was migrating huge and unwieldy mailboxes into the db at the time, so didn’t really have time to digest the warning.

That really looks like the sort of thing we might have seen on Exchange 2010, back in the day, but according to the literature, there is no 1024GB limit in Exchange 2013 standard, and never has been. The registry key referred to in Error event id 40011 doesn’t exist. So… what do we do? we follow the advice for Exchange 2010, here: How to prevent your Exchange Database Drives filling up completely and set the limit to, say, 3072GB. That’s not quite complete, though. It may work very well for 2010, but to get it to work in 2013 you need to use mount-database with the –force parameter. If you try and mount from the EAC (or without the –force) it will continue to fail. It will also need to be mounted with –force *every time*. ouch.

Which is why it’s worth writing  this blog article. Any database created with the RTM code will be affected by this, so anyone who has had Exchange Standard installed since the early days, or thought they had to install RTM and then install a CU on top of it, may see this problem as their databases grow. My advice is to consider moving mailboxes to a new database created  on a later CU.

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