It's obvious that a lot of work has gone into performance on XenForo, it can really hum along, especially when you are judicious in the use of add-ons. But it hits a major road block, and that is XF doesn't really scale terribly well over numerous servers out of the box. Unless you are using a SAN, then you just can't run XenForo on a large scale without modifications or third party add-ons. It's a pity because some of this is already catered for (eg memcached connectivity) and other things could be remedied very easily. For example I have modified our index.php to include the Zend Stream Wrapper for S3. It's a hack, but with just three lines I can run all external data on S3 (and the same hack would work for other architectures). I've also had to use xfrock's excellent attachment store. This bit concerns me, because without this add-on we'd be in serious trouble, and I dont like the idea that xfrocks might move on or the add-on becomes out-of-date. It's also a pain because every time we update, I have to reapply the same hacks to index.php, admin.php etc. So what I would suggest would be a good development, either built into the core, or an officially supported paid-for addon like Resource Manager that saves all data off the server and on to platforms such as S3 or Gluster leaving only the code. A code replication facility would be nice, but I am not so bothered about that.