Tiger: Disk-Adaptive Redundancy Without Placement Restrictions


Saurabh Kadekodi, Google; Francisco Maturana and Sanjith Athlur, Carnegie Mellon University; Arif Merchant, Google; K. V. Rashmi and Gregory R. Ganger, Carnegie Mellon University


Large-scale cluster storage systems use redundancy (via erasure coding) to ensure data durability. Disk-adaptive redundancy—dynamically tailoring the redundancy scheme to observed disk failure rates—promises significant space and cost savings. Existing disk-adaptive redundancy systems, however, pose undesirable constraints on data placement, partitioning disks into subclusters that have homogeneous failure rates and forcing each erasure-coded stripe to be entirely placed on the disks within one subcluster. This design increases risk, by reducing intra-stripe diversity and being more susceptible to unanticipated changes in a make/model's failure rate, and only works for very large storage clusters fully committed to disk-adaptive redundancy.

Tiger is a new disk-adaptive redundancy system that efficiently avoids adoption-blocking placement constraints, while also providing higher space-savings and lower risk relative to prior designs. To do so, Tiger introduces the eclectic stripe, in which redundancy is tailored to the potentially-diverse failure rates of whichever disks are selected for storing that particular stripe. With eclectic stripes, pre-existing placement policies can be used while still enjoying the space-savings and robustness benefits of disk-adaptive redundancy. This paper introduces eclectic striping and Tiger's design, including a new mean-time-to-data-loss (MTTDL) approximation technique and new approaches for ensuring safe per-stripe settings given that failure rates of different devices change over time. In addition to avoiding placement constraints, evaluation with logs from real-world clusters shows that Tiger provides better space-savings, less bursty IO for changing redundancy schemes, and better robustness (due to increased risk-diversity) than prior disk-adaptive redundancy designs.

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@inproceedings {280928,
author = {Saurabh Kadekodi and Francisco Maturana and Sanjith Athlur and Arif Merchant and K. V. Rashmi and Gregory R. Ganger},
title = {Tiger: {Disk-Adaptive} Redundancy Without Placement Restrictions},
booktitle = {16th USENIX Symposium on Operating Systems Design and Implementation (OSDI 22)},
year = {2022},
isbn = {978-1-939133-28-1},
address = {Carlsbad, CA},
pages = {413--429},
url = {https://www.usenix.org/conference/osdi22/presentation/kadekodi},
publisher = {USENIX Association},
month = jul

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