Then probably you are having the same issue that I had.
Because the fstab can not mount the drives, it can not mount the unionfs and it enters in an emergency state (I think is called like that).
The solution is to do a clean install and before reboot edit the /etc/fstab file and add noauto, in the options section, to all lines between [openmediavault]
to have something like :
/dev/disk/by-label/Disk1 /srv/dev-disk-by-label-Disk1 ext4 noauto,defaults,nofail,user_xattr,usrjquota=aquota.user,grpjquota=aquota.group,jqfmt=vfsv0,acl 0 2`
Edit also the /etc/openmediavault/config.xml
and add noauto in every <opts>
tag, just in case omv rebuilds the fstab
After that, edit /etc/rc.local
and add the mounts to your drives, something like
mount -o defaults,nofail,user_xattr,noexec,usrjquota=aquota.user,grpjquota=aquota.group,jqfmt=vfsv0,acl /dev/disk/by-label/Disk1 /srv/dev-disk-by-label-Disk1
and to your unionfs
mergerfs -o defaults,allow_other,cache.files=off,use_ino,category.create=mfs,minfreespace=15G,fsname=Stack:c0083937-7492-4afd-a975$d-a975-4516a61977d8 /srv/dev-disk-by-label-Disk1:/srv/dev-disk-by-label-Disk2:/srv/dev-disk-by-label-Disk3 /srv/c0083937-7492-4afd-a975-4516a61977d8
You can copy the names and the options from your fstab file