A Starting System Of Multiple Incremental Virtual Machines Based On Shadow Cache

When a large number of virtual machines are started at the same time in theenvironment where virtual disk images are stored centrally, the time will be long which ittakes for virtual disk images to be transferred from the hard disk to the memory becausethe hard disk I/O throughput capacity is limited. This eventually leads the virtual machinestart-up speed to be very slow.In order to solve the problem mentioned above, the starting system of multipleincremental virtual machines based on shadow cache, also named Scache, exploits thesimilarity between virtual machines used by consumers to provide virtual machines withvirtual block devices which are composed of basic image files and incremental image files.And through modification of asynchronous reading operations in Qemu block devicemodel on Xen4.1.2and building shadow cache that consist of multiple data-set-cachestructures, this system stores the data needed by the starting process of incremental virtualmachines in a specific data-set-cache structure so as to get incremental virtual machines toshare it during their starting process. Here every data-set-cache structure in the shadowcache corresponds to one of the basic images and is shared by multiple incremental virtualmachines that are created based on this basic image. Under such circumstances for virtualmachines, the memory cache hierarchy structure and the hard disk image file stackstructure is a one-to-one relationship, as if the former is the latter’s shadow. MeanwhileScache system also avoids repeatable read operations on the same data in shared basicimage files during starting process of incremental virtual machines.By concrete evaluation experiments, Scache system is able to minimize the load onhard disks and network during the starting process of incremental virtual machines.Moreover the starting process of incremental virtual machines has been acceleratedobviously in the role of this system and regardless of the configured memory size, thissystem costs only a small amount of extra memory on a basic image file shared by severalincremental virtual machines.