On Windows Server 2008-R2 File Servers with Access-Based Enumeration (ABE) enabled, you might notice abnormally high CPU-usage when many users are opening session or browsing through shared folder (and sub-folders) at the same time. Obviously this is caused by ABE enumerating folders the active user(s) are actually granted access to. This may become problematic when the underlying folder structure involves many sub-folders.
In an attempt to improve the situation (not a real performance fix), Microsoft has released a fix which enables more granular control on the number of folder levels ABE will take into account when processing a request. This fix and the details about the extra control it brings are available for download at the following location:
While installing the fix will require a reboot, you will also have to restart the LanmanServer service for the ABELevel parameter to be taken into account if you set it higher than 0 (default value if omitted). Note: you can actually set a value higher than 2.
As reminder, the article hereunder will help you keeping your Windows Server 2008-R2 File Server up-to-date with hot fixes: