2-Dimensional Erasure Coded LTO Tapes with RAIL Library configuration

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Publish Date: 
Tuesday, June 8, 2021
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Active archives enable media companies to quickly, efficiently and cost-effectively search their vast volumes of content to retrieve and process assets they need. Erasure coding can be used to protect this content, but it typically requires more resources and increases content retrieval latencies, limiting performance. This paper proposes a technology that offers higher content durability and availability with minimum latencies and less storage overhead than a two-copy scheme. INSIC Tape Roadmap forecasts 35% Areal Density and 25% Track Density CAGR, requiring future track pitches to be below 1000nm, such as a recently published 580TB tape technology demo requiring 50nm track pitch. At these dimensions, considering that tape must operate in open environmental conditions, drives and media failures will be dominated by correlated errors requiring more protection than an internal format erasure correcting code (ECC) and two-copy scheme can provide to achieve more than 11-nines durability.

Current replication techniques don’t provide resource-friendly protection and can’t meet 11-nines durability unless more than two copies are used. In a typical tape archival scenario, a carefully designed multi-dimensional erasure coding mechanism can bring novel efficient resource utilization, better availability and durability, and more environment-friendly operation for distributed tape systems with less overhead than two-copy protection. To reduce repeated read cycles and I/O bandwidth requirements, increase durability, and improve local recoverability, we propose multi-dimensional, hierarchical overlay erasure coding with interleaved codewords. Its unique mathematical coding structure and special interleaving allows local repair and almost uncorrelated errors, helping maximize local tape operations - i.e. minimize the system’s tape, drive and robot requirements.

Thanks to special metadata handling, the proposed system’s byproducts are the self-describing erasure-coded tapes friendly to disaster recovery and content transportation. These combined contributions help increase the lifetime of different subsystems of tape and improve the archival storage system’s performance.



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