Abstract

The write performance of multi-level cell (MLC) is several times slower than single-level cell (SLC); however, the cost per bit of MLC is much lower than SLC. Dual-mode flash (the medium can be partially switched to SLC mode by programming only 1 bit in some cells) can combine SLC and MLC to provide trading density opportunity for performance. In this paper, we present Hercules—a hybrid storage system that couples dual-mode flash memory and hard drive disk (HDD)—based on the content locality principle for high storage performance. The data are divided into two types: the reference data for read operation and the delta data for write operation. The reference data are stored in SLC and the delta data in MLC or HDD in sequential orders. Hercules organizes the metadata for the mapping of the physical locations of the reference blocks and the delta data of the original blocks, intelligently identifies hot/cold data and performs the data migration between MLC and disk for performance improvements. To validate our findings, we implemented Hercules and made evaluation to show that Hercules can effectively improve the data access speed and reduce the response time, compared with the Flashcache storage structure, and in particular, with Hercules, we can achieve 10% performance improvement over the system in absence of hot delta data caching.

中文翻译：

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Hercules：双模闪存和硬盘驱动器的智能耦合

摘要

多级单元（MLC）的写入性能比单级单元（SLC）慢几倍；但是，MLC的每比特成本比SLC低得多。双模闪存（通过在某些单元中仅对1位进行编程可以将介质部分切换到SLC模式）可以将SLC和MLC结合使用，从而为性能提供交易密度的机会。在本文中，我们介绍了大力神（Hercules） —一种混合存储系统，将双模闪存和硬盘驱动器耦合在一起（HDD）-基于内容本地性原则以实现高存储性能。数据分为两种类型：用于读取操作的参考数据和用于写入操作的增量数据。参考数据按顺序存储在SLC中，增量数据存储在MLC或HDD中。Hercules组织元数据以映射参考块的物理位置和原始块的增量数据，智能识别热/冷数据，并执行MLC和磁盘之间的数据迁移以提高性能。为了验证我们的发现，我们实施了Hercules并进行了评估，以表明与Flashcache存储结构（尤其是Hercules）相比，Hercules可以有效地提高数据访问速度并缩短响应时间。