Hello Damir.

If I try to create local storage, it works, but then host is in separate Data Center.
If I try to add POSIX FS to node in existing Data Center, then all other hosts stop working, since they can't access that local storage (kind of expected).

So, long story short - does shared and local storage mix and how?

We faced the same need - to use a local storage for our CI and managed to use vdsm scratchpad hook for that:

http://www.ovirt.org/VDSM-Hooks/scratchpad

it implements something similar to AWS ephemeral storage, so it mounts a local disk that does not survive over reboot. This might work for you. Of cause it will not be possible to migrate such a VM and the hook will fails an attempt to do migration.

Please note that there is a patch https://gerrit.ovirt.org/#/c/42573/ without which it may not work. This patch was merged, but most like is not yet at the ovirt version you use.

Let me know if you have other questions with regards to that hook usage. I may also share my unit files for systemd to format and mount the local storage provided by the hook.

Anton.