Solid state drives (SSDs) are normally constructed with a number of parallel-accessible flash chips, where host I/O requests are processed in parallel. In addition, there are many internal activities in SSDs, such as garbage collection and wear leveling induced read, write, and erase operations, to solve the issues of inability of in-place updates and limited lifetime. When internal activities are triggered on a chip, the chip will be blocked. Our preliminary studies on several workloads show that when internal activities are frequently triggered, the host I/O performance will be significantly impacted because of the
access conflict
between them. In this work, in order to improve the access conflict induced performance degradation, a novel
access conflict
minimization scheme is proposed. The basic idea of the scheme is motivated by an interesting observation in SSDs: several chips are idle when other chips are busy with internal activities and host I/O requests. Based on this observation, we propose to schedule internal activities induced operations for minimized access conflict by exploiting the idleness of the multiple chips of SSDs. This approach is realized by two steps: First, read internal activities accessed data to the controller; second, by exploiting the idle chips during internal activities, write internal activities accessed data back to these idle chips. With this scheme, the internal activities can be processed with minimized access conflict to the host requests. Simulation results show that the proposed approach significantly reduces the access conflict, and in turn leads to a significant performance improvement of SSDs.
The write performance of flash memory has been degraded significantly due to the recent density-oriented advancements of flash technology. Techniques have been proposed to improve the write performance by exploiting the varying strength of a flash block in its different worn-out stages. A block is written with a faster speed when it is new and strong, and gradually will be written with slower speeds as it is aging and becomes weak. Motivated by these works, this brief proposes a new technique by exploiting the significant process variation among flash blocks introduced by the advanced technology scaling. First, a write speed detection approach is proposed to identify the strength of each block. Then, a heuristic approach is proposed to exploit the speed variation among blocks for write performance improvement. A series of trace-driven simulations shows that the proposed approach generates substantial write performance improvement over state-of-the-art approaches by 30% on average.
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