I would suggest identifying the directories you expect to grow and have a separate mount for those. We have a zFS mount for the OnDemand libraries, mounted as read-only. Then we have a read-write mount for directories containing configuration files. Lastly we have separate mounts for directories like TEMP and CACHE so we can unmount/mount larger volumes if need be, especially for temp. For cache, which we don't use a lot, you can specify multiple cache filesystems. We half heartedly tried enlarging our temp space by adding a volume but couldn't get the mount to span volumes and just ended up defining a single MOD27.