Append is Near: Log-based Data Management on ZNS SSDs
Append is Near: Log-based Data Management on ZNS SSDs
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发表时间：
2022
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通讯作者：
Devashish R. Purandare;Peter Wilcox;Heiner Litz;Sheldon J. Finkelstein
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作者：
Devashish R. Purandare;Peter Wilcox;Heiner Litz;Sheldon J. Finkelstein
基于日志的数据管理系统使用存储就好像它是一个仅追加的介质，将随机写转换为顺序写，当日志持久化在硬盘上时，这将带来显著的好处。尽管固态驱动器（ssd）提供了改进的随机写入功能，但由于局部性和空间效率，顺序写入仍然具有优势。然而，当与随机写块接口一起使用时，基于闪存的ssd的固有属性会导致主要缺点，导致写放大、不均匀磨损、日志堆叠和垃圾收集开销。为了消除这些缺点，最近引入了Zoned Namespace (ZNS) ssd。它们提供了增加的容量，减少了写入放大，并通过区域向主机开放数据放置和垃圾收集，这些区域具有顺序写入语义，必须显式重置。我们解释了新的ZNS Zone Append原语，它支持将细粒度的数据放置到设备上，以及我们对“Group Append”的建议，它支持子块大小的追加，可以使日志结构的数据管理系统受益。我们在四个基于日志的数据管理领域探索了带有Zone Append、Group Append和计算存储的ZNS ssd的优势：(i)基于日志的文件系统，（ii） LSM树（如RocksDB）， （iii）数据库系统，以及（iv）事件日志/共享日志。在此基础上，提出了基于ZNS固态硬盘的数据管理系统的研究方向。
Log-based data management systems use storage as if it were an append-only medium, transforming random writes into sequential writes, which delivers significant benefits when logs are persisted on hard disks. Although solid-state drives (SSDs) offer improved random write capabilities, sequential writes continue to be advantageous due to locality and space efficiency. However, the inherent properties of flash-based SSDs induce major disadvantages when used with a random write block interface, causing write amplification, uneven wear, log stacking, and garbage collection overheads. To eliminate these disadvantages, Zoned Namespace (ZNS) SSDs have recently been introduced. They offer increased capacity, reduced write amplification, and open up data placement and garbage collection to the host through zones, which have sequential-write semantics and must be explicitly reset. We explain how the new ZNS Zone Append primitive, which supports pushing fine-grained data placement onto the device, along with our proposal for “Group Append”, which enables sub-block sized appends, could benefit log-structured data management systems. We explore advantages of ZNS SSDs with Zone Append, Group Append, and computational storage in four log-based data management areas: (i) log-based file systems, (ii) LSM trees such as RocksDB, (iii) database systems, and (iv) event logs/shared logs. Furthermore, we propose research directions for each of these data management systems using ZNS SSDs.