Although flash cells wear out, a typical SSD has enough cells and sufficiently sophisticated firmware that its lifetime generally exceeds the expected lifetime of its host system. Even under heavy use, SSDs last for years and can be replaced upon failure. On a smartphone, in contrast, the hardware is more limited and we show that, under heavy use, one can easily, and more quickly, wear out smartphone flash storage. Consequently, a simple, unprivileged, malicious application can render a smartphone unbootable ("bricked") in a few weeks with no warning signs to the user. This bleak result becomes more worrisome when considering the fact that smartphone users generally believe it is safe to try out new applications. To combat this problem, we study the I/O behavior of a wide range of Android applications. We find that high-volume write bursts exist, yet none of the applications we checked sustains an average write rate that is high enough to damage the device (under reasonable usage assumptions backed by the literature). We therefore propose a rate-limiting algorithm for write activity that (1) prevents such attacks, (2) accommodates "normal" bursts, and (3) ensures that the smartphone drive lifetime is longer than a preconfigured lower bound (i.e., its warranty). In terms of user experience, our design only requires that, in the worst case of an app that issues continuous, unsustainable, and unusual writes, the user decides whether to shorten the phone's life or rate limit the problematic app.
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Fair Write Attribution and Allocation for Consolidated Flash Cache
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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- Award ID(s):
- 1908793
- NSF-PAR ID:
- 10195415
- Date Published:
- Journal Name:
- Proceedings of the Twenty-Fifth International Conference on Architectural Support for Programming Languages and Operating Systems
- Page Range / eLocation ID:
- 1063 to 1076
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1145/3373376.3378502
