Feasibility study for building hybrid storage system consisting of non-volatile DIMM and SSD

Various vendors develop a byte accessible Nonvolatile Dual-Inline Memory Module (NVDIMM). The performance of the NVDIMM drastically surpasses that of the Solid State Drive (SSD), which is connected by PCI express. However, the cost of the NVDIMM is much higher than that of the SSD. Therefore, a hybrid storage system between the NVDIMM and SSD is an effective technique for improving cost-performance. If a system uses the NVDIMM less while maintaining performance, its cost-performance should be improved. Our previous work involves on-the-fly automated storage tiering (OTF-AST). OTF-AST is a hybrid storage system consisting of an SSD and HDD. It aims to reduce the average response time of IO accesses by migrating only the IO concentration area to the SSD when IO concentration happens. Therefore, we construct OTF-AST with both the DIMM and SSD and evaluate it in order to understand how to build a cost-effective hybrid storage system with these devices. We use a DIMM instead of a byte accessible NVDIMM, which is difficult to obtain. As a result, we found that the original OTF-AST is suitable for a hybrid storage system consisting of the DIMM and SSD. Moreover, we can improve the performance of OTF-AST if replace its migration algorithm with a more positive migration algorithm. This is because the IO access response time barely increases when the data migration between the DIMM and SSD is done. We will build a more positive migration algorithm in the near future.