The Storage Hierarchy is Not a Hierarchy: Optimizing Caching on Modern Storage Devices with Orthus


Kan Wu, Zhihan Guo, Guanzhou Hu, and Kaiwei Tu, University of Wisconsin–Madison; Ramnatthan Alagappan, VMware Research; Rathijit Sen and Kwanghyun Park, Microsoft; Andrea C. Arpaci-Dusseau and Remzi H. Arpaci-Dusseau, University of Wisconsin–Madison


We introduce non-hierarchical caching (NHC), a novel approach to caching in modern storage hierarchies. NHC improves performance as compared to classic caching by redirecting excess load to devices lower in the hierarchy when it is advantageous to do so. NHC dynamically adjusts allocation and access decisions, thus maximizing performance (e.g., high throughput, low 99%-ile latency). We implement NHC in Orthus-CAS (a block-layer caching kernel module) and Orthus-KV (a user-level caching layer for a key-value store). We show the efficacy of NHC via a thorough empirical study: Orthus-KV and Orthus-CAS offer significantly better performance (by up to 2x) than classic caching on various modern hierarchies, under a range of realistic workloads.

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@inproceedings {264852,
author = {Kan Wu and Zhihan Guo and Guanzhou Hu and Kaiwei Tu and Ramnatthan Alagappan and Rathijit Sen and Kwanghyun Park and Andrea C. Arpaci-Dusseau and Remzi H. Arpaci-Dusseau},
title = {The Storage Hierarchy is Not a Hierarchy: Optimizing Caching on Modern Storage Devices with Orthus},
booktitle = {19th {USENIX} Conference on File and Storage Technologies ({FAST} 21)},
year = {2021},
isbn = {978-1-939133-20-5},
pages = {307--323},
url = {},
publisher = {{USENIX} Association},
month = feb,