- 學位論文
基於疊瓦式硬碟高容錯儲存系統之研究
A Study of Storage System with High Fault Tolerance based on Shingled Magnetic Recording Drives
摘要
隨著雲端服務的發展以及行動裝置、物聯網裝置數量的成長，人們對於儲存空間的需求也與日俱增。而在如此需要儲存大量資料的情況下，如何去建置一個保有一定可靠度(reliability)與效能且價格低廉的大容量儲存系統(storage system)為本論文的主要研究目標。 一般而言，大多的儲存系統都建置於傳統硬碟之上，然而傳統硬碟技術在容量提升上已經遇到頻頸，無法應付不斷成長的儲存需求。因此，有了新興的磁碟技術出現，而其中最具競爭力，價格低廉的硬碟技術非 "疊瓦式磁紀錄(Shingled Magnetic Recording, SMR)硬碟" 莫屬。相較於傳統磁紀錄(Conventional Magnetic Recording, CMR)硬碟，因為SMR硬碟高儲存密度的特性，能夠達到高儲存量以及低成本的需求。同時，相較於使用CMR硬碟，使用高容量的SMR硬碟更能夠節省建置儲存系統所需要的物理空間。基於上述的理由，SMR硬碟很適合做為整個系統主要的資料儲存空間。 但由於SMR硬碟使用重疊相鄰磁軌(adjacent tracks)的方式來達到提升儲存密度(storage density)的緣故，對於隨機寫入(random write)的容忍度很低，進行資料寫入時會有寫入放大(write amplification)的問題。若單純使用SMR硬碟組成磁碟陣列以達成儲存系統的可靠性，勢必會因為頻繁更新資料(data)與同位編碼(parity)而造成系統寫入效能的瓶頸，使得系統無法提供良好的存取服務。 所以本論文提出一個基於SMR硬碟與LRC編碼的大容量儲存系統，我們利用Local Reconstruction Codes(LRC)作為儲存系統的容錯(fault tolerance)機制，因為LRC資料的重建(Reconstruction)成本比傳統Reed Solomon codes(RS codes)的方式低許多，容錯能力也相對比較好。同時，我們採用SMR與CMR硬碟混用的架構，使系統在降低成本的情況下保有一定的效能。而為了要更進一步提升儲存效能，本論文設計了一套資源管理機制，以管理資料與同位編碼的儲存與更新，來減少因採用SMR硬碟所造成的效能下降問題。 實驗數據顯示本論文所提出的磁碟架構相較於單純的SMR磁碟陣列能大大降低資料寫入的時間，而透過提出的管理機制則讓系統的效能更加提升。
並列摘要
The demand for storage space grows as cloud services, vast amounts of mobile and IoT devices emerge. To provide high capacity with reasonable reliability and performance while keeping the low cost is the major purpose of this research. In general, conventional magnetic recording drives are used to construct storage systems; however, the conventional disk drives cannot handle the non-stopping demand for storage space due to the physical limitation of itself. Therefore, some emerging magnetic recording techniques are proposed in recent years and Shingled Magnetic Recording technique is the most promising of them due to its low cost. SMR disk drives can provide higher capacity with lower cost compared to that of conventional disk drives. Hence, use SMR drives as the major storage components in the large storage system is a good solution. However, SMR drives overlapped adjacent tracks to increase storage density, which leads to write amplification problem. Utilize SMR drives as storage components in RAID to build to a fault-tolerant storage system can lower the system performance greatly, since updating parity frequently can even degrade the write performance. Therefore, in this thesis, a high capacity storage system based on SMR drives and Local Construction Codes is proposed. First, in the proposed system, LRC is applied as the fault-tolerant mechanism, because of that the system reconstruction overhead of LRC is lower than that of Reed Solomon Codes when a disk failure happened. Then, SMR drives and CMR drives are utilized to store data and parity, respectively for enhancing the system performance and decrease the cost. Finally, a resource management mechanism is proposed to handle the read, write, and update request of data and of parity to enhance the overall access performance. The simulation results show that the proposed system can greatly improve the access performance compared to pure SMR RAID system. In addition, the proposed resource management mechanism can further reduce the write amplification effect of SMR drives and enhance the system efficiency.
參考文獻
延伸閱讀
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