Consolidating multiple workloads on a single flash-based storage device is now a common practice. We identify a new problem related to lifetime management in such settings: how should one partition device resources among consolidated workloads such that their allowed contributions to the device's wear (resulting from their writes including hidden writes due to garbage collection) may be deemed fairly assigned? When flash is used as a cache/buffer, such fairness is important because it impacts what and how much traffic from various workloads may be serviced using flash which in turn affects their performance. We first clarify why the write attribution problem (i.e., which workload contributed how many writes) is non-trivial. We then present a technique for it inspired by the Shapley value, a classical concept from cooperative game theory, and demonstrate that it is accurate, fair, and feasible. We next consider how to treat an overall "write budget" (i.e., total allowable writes during a given time period) for the device as a first-class resource worthy of explicit management. Towards this, we propose a novel write budget allocation technique. Finally, we construct a dynamic lifetime management framework for consolidated devices by putting the above elements together. Our experiments using real-world workloads demonstrate that our write allocation and attribution techniques lead to performance fairness across consolidated workloads.
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Append is Near: Log-based Data Management on ZNS SSDs
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 advan- tageous 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 amplifica- tion, uneven wear, log stacking, and garbage collection overheads. To eliminate these disadvantages, Zoned Namespace (ZNS) SSDs have recently been introduced. They offer increased capacity, re- duced 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 sup- ports 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 sys- tems. 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.
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- NSF-PAR ID:
- 10315205
- Date Published:
- Journal Name:
- 12th Annual Conference on Innovative Data Systems Research (CIDR ’22).
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
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