ESXi Ova/OVF templates upload on Glance

Hello,
I'm deploying Openstack with basic components (using Nova, Keystone and Glance) for provisioning VMs using ESXi as hypervisor.

Everything works fine, except for the fact that i don't know what is the correct way to upload on OVA file (or OVF template) on glance in a way that can be used by nova to provide correct provisioning of the VMs.

 What I have done so far is uploading flat .vmdk disks (downloaded directly through vSphere) and everything works, but the image is oversized (as much as the disk assigned to that VM) and the provision is very very slow.

 So what i want to do is to use OVA/OVF templates exported from ESXi in order to easly create my own custom images and be able to provision them in a reasonable amount of time (which should be true considering the dimension is dramatically lower).

And here is the question: what is the right way to upload OVA/OVF using glance? I've tried something like this for an OVA file:

glance add name="LinuxWS-OVA" disk_format=vmdk container_format=ovf vmware_adaptertype='lsiLogic' vmware_ostype="ubuntu64Guest" < OpenstackTest.ova

And the upload goes correctly, but when i deploy the VM it comes up without OS (using vSphere console all i get is "Operative System not Found."
I also have an OVF templace (consisting of 3 files: .vmdk .mf .ovf) but i don't know how should i upload them to let glance understand that they are part of the same template.

Any idea? Is it only possible to use ESXi as Hypervisor through super-sized flat .vmdk? thanks for your answers.