Virtualizing Storage as Memory for High Performance Storage Access

The advance of the technologies surrounding non-volatile memory (NVM) storage brings the significant improvement of its performance. While such hardware technologies progress, the software technologies for storage stagnate. The current I/O architecture of the operating system (OS) kernel to interact with storage devices was designed a long time ago when HDDs were very slow, and is beginning to cause a mismatch with high performance NVM storage. Such a mismatch is further exaggerated in virtualized environments since the software layers duplicated in a guest and its host kernels create a long I/O request processing path. Because virtualized environments play an major role to enable cloud computing and also because big data processing requires high performance storage access, the I/O architecture for virtualized environments has to be reorganized in a way that it can fully utilize the high performance of NVM storage. This paper proposes a novel storage virtualization method that virtualizes storage as memory, so that virtualized storage provides memory interface. We call such storage virtualized as memory virtual main memory storage (VMMS). VMMS removes the duplication of I/O software layers, and significantly shortens the I/O request processing path. VMMS was implemented in Linux that employs KVM (Kernel-based Virtual Machine) as virtualization software. The evaluation results of VMMS performed on a RAM disk drive and a SSD show that VMMS enables the significant reduction of I/O costs and scales much better than the current I/O architecture.

I. Introduction

The advance of the technologies surrounding non-volatile memory (NVM) storage brings the significant improvement of its performance. Flash memory ¹

In this paper, flash memory stands for NAND flash memory.

can achieve higher performance by exploiting the parallelism of devices and a devised mapping scheme that can take advantage of it [1]. New NVM technologies, such as PCM (phase change memory), MRAM, and ReRAM, inherently provide higher performance [2], and they can be combined with flash memory in order to achieve both high performance and large capacity. The next generation I/O bus and controller interfaces, such as PCI-Express Gen 3 and NVM-Express [3], will further accelerate storage access performance.