Thanks for that Jason
Yes I can see no issues with DFSR even though we are replicating the whole dirroot. However the two issues are disk space as we need 3 times the normal space and also the fact that its a lot of data to move around should we need to. I mean rebuilding a server that has a shared dirroot is as simple as mounting or pointing moodle at the old dirroot.
Twice this summer we have had to copy it to another server, when adding new nodes or migrating to new servers. This can take 8 hours!