Empirical study of virtual disks performance with KVM on DAS

There is exponentially increasing demand of data generation, its storage, access and communication. To fulfil the demands, concept called Cloud Computing came into the picture. The key concept operating at the basic level of cloud computing stack is a Virtualization. Virtual machine (VM) state is represented as a virtual disk file (image) that is created on the hypervisor´s local file system, from where virtual machine is booted up. Virtual machine requires minimum one disk to boot and start its function. Within guest operating system, one can use block devices or files as virtual disks with Kernel-based Virtual Machine (KVM). Till the time, no empirical study has been performed on different types of virtual disk image formats to quantify their runtime performance. We have studied representative application workload: I/O micro-benchmarks on a local file system i.e. direct-attached storage (DAS) environment in conjunction with RAW, Copy-on-Write scheme QCOW2 from QEMU, Microsoft´s VHD, Virtualbox´s VDI, VMWARE´s VMDK and parallel´s HDD. We have also investigated the impact of block size on applications runtime performance. This paper seeks to provide the detailed runtime performance analysis of different image formats based on different parameters such as latency, bandwidth, IOs performed per second (IOPS). Today users have a choice to select virtual disks from the pool of virtual disk image formats. But, currently it´s a black box selection for users as no comparison or decision model exist for different virtual disk image formats. This study is done to provide insights into the performance aspect of various virtual disk image formats and offer guidelines to virtual disk end users in implementing and using them respectively.