Design And Implementation Of Hybrid Storage Scheme Based On Flashcache

Computer technology is developing rapidly, but the acess speed of HDD(Hard DiskDriver) is improving slowly, thus the acess speed become a mainly factor impact on theperformance of computer system. The rapid development of SSD as a new type of storagemedia injected new vitality to the storage system. The read and write speeds of SSD is fast,especially random I/O capability of SSD is very good, but compare to traditionalmechanical hard disk it’s expensive and capacity is much smaller. Open source projectflashcache is an implementation of the hybrid storage technology, it uses the SSD as acache between disk and memory to achieve performance enhancement. Currentlyflashcache has some deficiencies and can be further improved.Of depth analysis to flashcache and the combination of SSD characteristics, andconsidering performance and data reliability, this paper propose an improve methods toflashcache. Instead of flashcache’s set management methods,we use Radix Tree structureto management cache, so we can globally deploy SSD cache block to improve SSDutilization and cache hit rate. We use double LRU list to identify hot spots cache block,reuse non-hotspot cache block of address adjacent while the cache block to be replaced toretain the most cache block, thus can make the write to SSD close to chunks, achievebetter write performance and lenthen the using life of SSD. We introduce NVRAM to savethe cache blocks metadata real-time change, on the one hand can ensure the datavalidation, on the other hand to avoid impact on hybrid storage system performance due tothe real-time metadata being written to the SSD.We implemented the improved methods base on flashcache, and did a compare test.The test result shows that compare to pure HDD scheme hybrid storage can effectivelyimprove data access speed, and reduce access response time, and the improve method canfurther improve the performance.