I have a simillar "problem" with my setup. I have two backup disks scheduled for weekly rsync tasks, and both are under samba shares. I am connecting these disks manually to my OMV machine only for backup purposes.
Because of that I have a lot Syslog and Demon logs - 36 entries in one minute.
Maybe there is some safe wat to unmount this kind of disk in the system without disabling all sharing points?
No there isn't. The usage of temporarily added drives for services is very uncommon. This is simply not how a server is supposed to work. So if you insist in doing it this way, you gonna have to disable shares and unmount manually. Of course you could just program it yourself but this is not going to be easy.
But again, error messages are not a problem. A problem is misusage by disconnecting mounted drives. The error messages is just your server telling you that sth bad happened.