An Economic Perspective of Disk vs. Flash Media in Archival Storage

Abstract

For three decades, Kryder's law correctly predicted an exponential increase in bit density on disk platters, leading to an exponential drop in cost per gigabyte, and thus to an entrenched expectation that if data could be stored for a few years the incremental cost of storing it forever would be minimal. However, disk now is over 7 times as expensive as Kryder's law would have predicted, and industry projections suggest that in 2020 the gap will reach 200 times, disrupting this expectation. Our model shows that archives based upon alternative media are surprisingly cost competitive with archives based upon traditional disk media over the long-term. We propose using Archival Flash for long-term data preservation, with the trade off between longer data retention period and lower write cycles.