Itamar, The below, provided by David Lutterkort, is a good description of the requirements for Aeolus instance data injection. Joe VLcek RHEV-M shall accept a small blob of data as part of the 'start VM' action. That data has to be placed somewhere where the VM can easily and securely access it. The data must only be visible to the VM it is intended for. Possibilities for where to put the data include placing it into a file on a virtual floppy or CD-ROM that the instance can mount, or posting it on a webserver that only the instance has access to (cf. EC2's handling of userData for the RunInstances call) The size limitation for the amount of data shouldn't be kept artificially low, but if there are important reasons to make it this small 1k would certainly suffice. In practical terms, the blob of data should be passed to the 'start VM' call base64 encoded, and RHEV-M should decode it just before putting it into its proper place.