I recommend everyone using XenServer to move to XCP-ng [0]. They take the XenServer sources, remove licensing restrictions and add some great new features etc (like nfs4.1, ZFS etc.). They're from the same people behind Xen Orchestra (web-based console for XenServer) [1], and offer pro support like Citrix [2].

I was about to move off XenServer with the recent changes to licensing [3] (tl;dr they removed a bunch of features from the free edition), but XCP-ng has allowed me to continue with XenServer whilst make few changes to my already-working setup.

[0] https://xcp-ng.org/

[1] https://xen-orchestra.com/#!/xo-home

[2] https://xcp-ng.com/

[3] https://xenserver.org/blog/entry/xenserver-7-3-changes-to-th...