We have always installed ArcGIS server on windows - since 9.3.
We are at a point where we want what is most efficient. There is no clear examples out there on which is the better OS for ArcGIS Server.
Any feedback on this topic?
Thanks in advance.
This is more a religious issue than a technical one. Esri supports both Linux and Windows platforms, without regard to which one is "better".
There are a few technical issues which could steer you to one platform or the other (e.g., Direct Connect to MS SQL Server enterprise geodatabase is not possible from Linux, or the only version of Windows supported by your IT department is under the minimum or over the maximum required for ArcGIS), but from my experience, Server is startlingly OS agnostic.
Utilizing a new OS may have a ramp-up cost (if it's new to your IT infrastructure), but once the install is complete, the Server software behaves the same from a client standpoint. The usual hitches in porting between platforms are tied to customized extensions and the curious way case dependency is handled when migrating from case-neutral path strings of Windows to case-dependent paths in Linux.
Do you know if Enterprise GIS environment federated to portal can be of mixed OS? Or Is it recommended that all servers portal, arcgis server, web adaptor be of the same OS?
Communication between the portal and the GIS Servers all happens over HTTP, so as long as server and portal can talk to each other, you should be OK. You can mix OS's with Server/Web Adaptor and Server Portal, but not between servers that all participate in a single site because of file pathing issues like Vince mentions above. Those come into play when there's a shared config-store. I'd even try to keep the hardware identical if for the GIS Server site, if possible.
Personally, while I might have the web tier as Linux (for the web adaptor) for whatever reason (LDAP integration and licensing cost comes to mind), I'd keep the GIS tier homogeneous in terms of OS just to limit potential training issues.
Take note that backing up your deployment with the Web GIS DR tool won't work, as all components need to write to the same path exact path, (same string), which won't be the case if you have mixed OS.