I have installed Front End on disk image of only 100 GB. Thus, any attempt to upload (via Web) any QCOW2 of meaningful size simply fails because not enough space. However, I have 2 nodes up and running with terabytes of free storage in /var/lib/one, but have no idea how to specify storage for example on node on-node11.lcl. By default Web Upload uses disk image of the Front End. I can use command line but found no way how to specify for example storage on KVM host on-node11.lcl. On oVirt I used Export Storage Domain which could be on any NFS share, yet in Open Nebula this organized somehow different.
Unfortunately the import must be on a filesystem of the frontend, but you can mount (i.e. via nfs or sshfs) some of the storage on a directory of the frontend (oneadmin must be able to read that directory) and add it as a safe path of the image datastore.
After that, you can copy the qcow image to that safe path and add the image pointing to the path where it has been saved.