But there's nothing stopping you from enlisting Azure PV's as a resource, Ceph managed PV's, and other incantations of durable storage. I only ask that you really consider the cost/benefit of each, and pick what makes the most sense to you.
My thoughts would be to use the azure PV disk type, and if that's not dynamic enough to meet your needs, then enlist ceph + large volumes and carve those up into RDB's to share among your workloads.
I'm sure there are others with differing opinions, and I'm happy to help you work through them (but not on a HN comment thread)
Seek me out in Slack as @lazypower, or ping me on the Juju IRC channel irc.freenode.net #juju I'm @lazypower there as well.
And finally, our juju user mailing list is another great resource for supporting questions like the above:
juju@lists.ubuntu.com