For those of you with Exchange 2013 on Server 2012 RTM (not R2), you will run across two additional prerequisites while upgrading to the latest cumulative update.
The first prerequisite is a hotfix for the Resilient File System (KB 2894875). While it was only with the advent of Exchange 2016 that ReFS made it into the preferred architecture, ReFS was supported in Exchange 2013. Whether or not you are using ReFS you are still required to get the update. The hotfix addresses an issue where the operating system can freeze while trying to perform a DIR command on a ReFS volume. Nuts huh?
The second prerequisite is a hotfix for the Virtual Disk Service (KB 2884597). To quote Microsoft.
That does not sound good!
Download the fixes
For more information and to download both hotfixes check these links:
The hotfixes are only available by registering an email address to download.
Both fixes will require a reboot once you install them. The installer will also stop you from continuing until you have them.