| Summary: | 碩士 === 淡江大學 === 電機工程學系機器人工程碩士班 === 106 === In recent years, Non-volatile random-access memory (NVRAM) is regarded as a great alternative storage medium because of its beneficial features, including byte addressability, non-volatility, and short read/write latency. In addition, multi-level-cell (MLC) NVRAM was proposed to provide higher storage density.
Meanwhile, in the conventional Journaling File System (JFS), the storage space is divided into two regions, i.e. journal region and data region. To ensure data integrity, the data of JFS are written into journal region first during the commit operation. Data written to the journal region will be enclosed and tracked by a transaction structure, which records both the modified metadata and data content. And the transaction is regarded as a valid one only if it contains both the transaction header (H) and transaction tail (T) to indicate the start and the end points on storage. Then the Transaction pass the Checkpoint operation will be written to the data area. Hence, the same data will be written into storage twice in the Commitment operation and Checkpoint operation. Although JFS enhances the data safety, it also induces the data amplification problem. To mitigate the negative impact of the lengthened write latency of MLC NVRAM on existing JFS, we presents the journaling file system with multi-write mode (mwJFS) to boost the access performance of MLC NVRAM-based JFS.
The proposed mwJFS introduces a four-level data retention model to satisfy the retention requirement of different data types and applies suitable write modes for each retention level. The retention levels are defined in four levels: minute, hour, day and month. The system will take different write operations on MLC NVRAM for different data retention times. For example, the proposed method can use Heavy Write to make data save for a longer period or use Light Write to make data retention time and write Latency shorter than Heavy Write. In addition, a compressible check model is included to classify file data. A retention monitor mechanism and an incremental retention strategy are also included to check the residual data lifetime and refresh when necessary.
The experimental results show that the proposed system can differentiate the data retention requirement of journaled data and applies different write modes to enhance the access performance with lower energy consumption effectively. The mwJFS can reduce the burden of NVRAM and improve overall performance.
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