An Optimized COW Block Device Driver in VMM for Fast, On-Demand Software Deployment

The COW (copy-on-write) virtual block device supported by many virtual machine monitor (VMM) is very helpful for fast software deployment in large-scale virtualized computing environments. This paper presents an optimized block addressing approach for the COW block device driver in VMM and an on-demand software deployment scheme based on the optimization approach. With our approach, many small-sized COW disks can be made without impairing the access performance of the COW disk, and the small-sized COW disk can greatly reduce the cost of distributing software images to end-users over the network. We have developed a new block device driver mcow to implement the optimization approach in QEMU virtual machine monitor on Linux system. Experiments show that the mcow driver outperforms the original cow driver in QEMU especially in the case of deep COW disk hierarchy.