The target is for user to import .qcow2 image from download site and automatically stored as raw image. Read through [1], this seems doable. I am not sure the workflow. Does it download the whole qcow2 and convert it to raw locally, or download, convert and upload in a streaming way, which only require small space for caching? The question is that, how much local disk space is required for such import and conversion?
Yep, local disk space is required and must be large enough to handle the whole conversion (i.e. the qcow2 plus the converted image). Keep in mind that multiple users could be doing the same, so the disk space requirement may be large.
Also note that if you either need to configure the local self-reference URL[1] per worker (if you are running a recent-enough release) or that storage needs to be shared amongst all the workers for proper operation.
--Dan
1: https://docs.openstack.org/glance/latest/admin/interoperable-image-import.ht...