Hi,

I'm wondering at the moment what the actual difference is between
Shared and Local Storage Datacenters.

​By definition, taken from here [1],
Local storage:
When you set up a host to use local storage, the host automatically gets added to a new data center and cluster that no other hosts can be added to​.
Multiple host clusters require that all hosts have access to all storage domains, which is not possible with local storage.
Virtual machines created in a single host cluster cannot be migrated, fenced or scheduled.

Shared storage:
Set up NFS shares that will serve as a data domain and an export domain.
Storage data domains can be unattached from a data center and imported to another data center in the same environment, or in a different environment. Virtual machines, floating virtual disk images, and templates can then be uploaded from the imported storage domain to the attached data center.
 
As far as I can see a Local DC supports NFS as well which makes it a
more flexible DC in storage if you ask me, so why do both still exist
?

In fact by setting a local DC, only one host can be added and there's no high availability functionality.
According to [2], a local DC supports NFS shares for migration needs.
In case of sharing resources between more that one host, you should use a Shared DC.
 
Is it possible in a decent way to change a running Shared Storage DC
to a Local one and Keep the NFS shares and add some local mounts for
specific hosts ?

​Since a shared DC can support more than one host (while local DC supports exactly one), it's not possible moving from 'Share' type to a 'Local' type.​
 
I hope someone can clearify!
​Hope it makes more sense.​
 

​​
[1] https://www.ovirt.org/documentation/admin-guide/chap-Storage/
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1302185

Regards,
Shani Leviim​