komljen

I would say that there is just a little overhead as Postgres data volume is mounted inside Docker container. Running Postgres in docker container without volumes would have a bigger impact.

And Docker container is not a VM, so I don't like to use word Virtualization for containers :)

If you think that this is just new cool thing, you probably didn't read a lot about it. Can you run 20 WordPress isolated installations in 30 seconds on traditional way (20 MySQL servers and 20 Apache web servers on one host)? Or just commit changes you made on your installation push it to docker index, pull it on another host and run that? Without db and app backup and restore procedure and you have exactly the same environment on both hosts. So you don't care about MySQL, Apache all libraries on another host, their versions, etc. You are moving software, in this case WordPress with your environment. With docker environment and software are in one piece. It is all about that.

Maybe WordPress just isn't great example, but this is extremely useful for development (works locally) and for continuous integration process. Every time you install software on fresh environment, so you don't need to manage it.

It is not a scam...

Correct, Ceph is much larger than the file system. As I said at beginning of article I'm using each Ceph component, RBD, RadosGW and CephFS and I will write article for each of that. This is just some sort of getting started guide. I'm interested at running Hadoop on top of CephFS, is it stable enough?