Assessment of DM-cache Running on Virtual Linux

The amount of data located in storage servers increases continually with the growth of cloud and social networking services. Storage systems with very large capacities are prone to poor reliability and long latency, which can be addressed by using hybrid disks that contain both mechanical and flash memory storage. In Linux, these two types of device can be combined using a caching technique provided by the device mapping DM-cache utility. We evaluated the performance of DM-cache when Linux is running in native mode and on a virtual machine (VM). We identified problems with the response of the caching policy to a range of commands. We found that DM-cache reduces I/O latency when Linux was running in native mode, but the overheads incurred by caching actually reduced performance when Linux was installed as a guest operating system.