Don't bother with Writable Volumes on XenApp, I found this:
"App Volumes writable volumes are not pertinent to a XenApp implementation. A writable volume is created
solely for use in a one-to-one, rather than one-to-many, environment—that is, a writable volume is assigned
to only one user, whereas an AppStack can be assigned to many XenApp servers. XenApp in turn assigns the
AppStack-stored applications to many users."