The storage layer includes the repository of VM images, i.e. virtual disks containing a bootable operating system and additional applications. Patient-specific VMs are simple instances of these VM images. In order to publish new VM images, software vendors go through the following procedure: first, they clone an existing VM containing the right operating
system and perhaps some additional libraries of interest through the MyPHRMachines Web portal. At this stage, only
the vendor can instantiate the VM image and modify the VM image (install new software, adjust configuration files, etc.).
Finally, the vendor “publishes” the VM image for other users of MyPHRMachines. Users cannot change the published VM
image since any personal instance of a VM image is stateless. By keeping VM instances stateless, one can deploy updates at the VM image level, which is much more scalable and secure than trying to do this at the level of patient-specific VMs