Use nfsroot for diskless clients AND persistent storage

[Thomas]

Hi,
after successfully setting up FAI server version 5.9.4 I continued with
configuration for using nfsroot for diskless clients following this
<https://wiki.fai-project.org/index.php/Use_nfsroot_for_diskless_clients>
wiki article.

This is working without problems, too.

However, the diskless client (in my case KVM instance for testing) has
*no persistent storage*.
Any change written is gone after client is rebooted.

Therefore my question is:
How can I configure FAI nfsroot to save changes in client persistently?
Is this related to NFS version?
(I'm using NFSv4 only according to this
<https://wiki.debian.org/NFSServerSetup> guide.)

THX