Study On Hybrid Storage Systems

Nowadays, the development trend of storage systems tends to be of massstorage, low cost and high performance, while any kind of storage device,such as Non-Volatile Random Access Memory (NVRAM), Solid State Disk(SSD) and Hard Disk Drive (HDD), cannot meet the needs of these demandsmentioned above due to its intrinsic characteristics. Hybrid storage systems,built by making the most of the properties of different types of storagedevices, are not only capable to substantially extend the storage capacity, butalso able to remarkably improve the performance while keeping a lowsystem cost. Therefore, hybrid storage is becoming the developmentdirection of storage technology.In this thesis, the concept, development history and challenges of hybridstorage systems are introduced, based on which a hybrid storage systemnamed Trident is designed and implemented. The thesis is focused on thefollowing aspects:(1)The development history of hybrid storage systems is studied and adeep analysis on the critical technology problems in hybrid storage systemdesign is made.(2)Trident, a hybrid storage system based on NVRAM, SSD and HDDis designed and implemented, the issues of which includes architecture,mapping policy, hot data identification, data migration and so on.(3)Synthetic workload and production workload are used to test and compare the random and sequential access performance of HDD-only,Facebook FlashCache, and Trident storage systems. The cache hit rates arealso compared between FlashCache and Trident systems.The test results show that, to the Trident system, the sequential accessperformance is close to that of HDD-only storage system, the IOPS partiallyexceeds that of FlashCache, and the cache hit rate is close to that ofFlashCache with fewer write to SSD compare to FlashCache. This system isimplemented as a kernel module in the Linux OS and is transparent to upperlayer applications. The research achievement of this thesis provides areference for the design and implementation of other hybrid storage systems.