macOS Server 5.2, XSAN 5, and El Capitan

The Xsan client is built-in to the OS X nee macOS operating system. According to this Apple article Xsan versions included with or required by OS X - Apple Support El Capitan includes Xsan 4.1 and while it has not been updated to reflect Sierra it would appear Sierra includes Xsan 5.0. If you use StorNext you should also refer to Compatibility of SAN clients with Xsan and StorNext controllers - Apple Support which covers what Xsan version is compatible with which StorNext version.

I found this Compatibility of Xsan metadata controllers (MDCs) and clients - Apple Support which seems to have good news. It seems that if you have a macOS Sierra Mac running Server.app 5.1 and therefore Xsan 5.0 acting as the Meta Data Controller (MDC), then Xsan 4.0 and 4.1 clients can connect to it. This would mean El Capitan and Yosemite clients would be able to connect to it.

It is also possible to run Server.app 5.2 on El Capitan 10.11.6 although I am not convinced this will result in it using Xsan 5. However El Capitan and Yosemite clients would still be able to connect to it. I do not know what would happen if you tried using a Sierra client to connect to an El Capitan server which would Xsan 5.0 trying to (potentially) connect to a Xsan 4.1 server.