Design and Implementation of a Non-volatile RAM Disk in the SAN Environment

Abstract. The mechanical nature of the magnetic disks limits the possi-bility of significant improvement of the I/O performance of the magnetic disk storage systems currently in use. The use of magnetic disk stor-age system has become an obstacle to the performance development of critical applications. This paper describes an implementation of a remote non-volatile RAM disk (abbreviated as NVDisk) over Fiber Channel net-work. Read and write latencies are drastically reduced and thus the I/O performance of the storage system is improved by order of magnitudes. We implemented an NVDisk target driver to provide full standard SCSI command set support, so a virtual disk can be constructed for use in the storage area network. NVDisk does not engage the foreground server’s CPU and main memory resources, so it can undertake extremely heavy workloads. In addition, we implemented a Virtual Disk (VD) module in the Linux kernel, which used a memory pool and backup disks to form a virtual transparent appliance and achieved the encapsulation of the ramdisk. With this, snapshot-based online backup mechanisms can be carried out.The whole system was built in the FC SAN environment, so the NVDisk is fine scalable and can be shared easily between servers.