US Patent 8490088 On demand virtual machine image streaming

On demand image streaming (ODS), in one aspect, may perform both copy-on-write and copy-on-read to gradually bring data on remote storage server to a host's local disk. Prefetching may be performed during the time the resources are otherwise idle to bring in data from the remote storage server to the host's local disk. A new image format and the corresponding block device driver for a hypervisor or the like may be also provided. ODS' image format may include a header and a bitmap that indicates whether the data sectors are on local disk or remote storage server, and an image content, for instance, stored in raw format.