Apple has a new Xsan 2.1 update and as always the case make sure you are not in the middle of a production or serious work when updating especially in a San environment unless you absolutely need a fix brought by the update.  Kbase article on Xsan 2.1 update Download Link Xsan 2.1 

About Xsan Filesystem Update 2.1The 2.1 update is recommended for all systems running Xsan 2. This update includes general file system fixes, as well as specific fixes for:- metadata controller reliability- using and validating file system Access Control Lists- upgrading from Xsan 1.4

Important: Read before installing

• Xsan 2.0 and Mac OS X 10.5 or Mac OS X Server 10.5, or later, is required in order to install Xsan 2.1. Mac OS X 10.5.3 or Mac OS X Server 10.5.3 or later is recommended for this update.
• If you are setting up a new Xsan deployment, please see this article for the proper installation order.
• Be sure that all Metadata Controllers (MDCs) are updated before you make any configuration changes.
• Before installing, please review the Xsan 2 Migration Guide.
• During installation, do not change any Xsan settings, whether using Xsan Admin or a command-line tool.