论文标题

通过优化读取(扩展摘要)来减少固态驱动器读取潜伏期

Reducing Solid-State Drive Read Latency by Optimizing Read-Retry (Extended Abstract)

论文作者

Park, Jisung, Kim, Myungsuk, Chun, Myoungjun, Orosa, Lois, Kim, Jihong, Mutlu, Onur

论文摘要

带有高级多级单元格技术的3D NAND闪存提供了高存储密度,但由于大量的重新读取操作,遭受了显着的性能降解。尽管读取机制对于确保现代NAND闪存的可靠性至关重要,但它可以通过引入多个重试步骤,以通过调整后的读取引用电压值再次读取目标页面,从而大大增加SSD的读取潜伏期。通过对160个真实3D NAND闪存芯片的读取机制和严格表征的详细分析,我们通过利用现代NAND基于NAND FLASH的SSD中广泛采用的两个高级功能来找到新的机会来减少读取潜伏期:1)CACHE READ命令和2)强大的ECC引擎。首先,我们可以使用高级缓存读取命令来减少读取延迟,该命令允许NAND闪存芯片以管道的方式执行连续读取。其次,在最终的重试步骤中存在较大的ECC能力余量,可用于降低芯片级读取延迟。根据我们的新发现,我们开发了两种新技术,可有效地减少重新延迟的延迟:1)管道读取的读取(pr $^2 $)和2)自适应读取(AR $^2 $)。 pr $^2 $通过使用CACHE READ命令进行输送连续重试步骤,从而减少了重新读取操作的延迟。 Ar $^2 $通过根据确定ECC可容纳余量的当前操作条件而动态降低芯片级读取延迟,从而缩短每个重试步骤的延迟。我们使用十二个现实世界的工作负载进行评估表明,我们的提案在最先进的基线中提高了SSD响应时间高达31.5%(平均为17%),而SSD控制器只有很小的变化。

3D NAND flash memory with advanced multi-level cell techniques provides high storage density, but suffers from significant performance degradation due to a large number of read-retry operations. Although the read-retry mechanism is essential to ensuring the reliability of modern NAND flash memory, it can significantly increase the read latency of an SSD by introducing multiple retry steps that read the target page again with adjusted read-reference voltage values. Through a detailed analysis of the read mechanism and rigorous characterization of 160 real 3D NAND flash memory chips, we find new opportunities to reduce the read-retry latency by exploiting two advanced features widely adopted in modern NAND flash-based SSDs: 1) the CACHE READ command and 2) strong ECC engine. First, we can reduce the read-retry latency using the advanced CACHE READ command that allows a NAND flash chip to perform consecutive reads in a pipelined manner. Second, there exists a large ECC-capability margin in the final retry step that can be used for reducing the chip-level read latency. Based on our new findings, we develop two new techniques that effectively reduce the read-retry latency: 1) Pipelined Read-Retry (PR$^2$) and 2) Adaptive Read-Retry (AR$^2$). PR$^2$ reduces the latency of a read-retry operation by pipelining consecutive retry steps using the CACHE READ command. AR$^2$ shortens the latency of each retry step by dynamically reducing the chip-level read latency depending on the current operating conditions that determine the ECC-capability margin. Our evaluation using twelve real-world workloads shows that our proposal improves SSD response time by up to 31.5% (17% on average) over a state-of-the-art baseline with only small changes to the SSD controller.

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