Data placement techniques for serpentine tapes
Ali E. Dashti, Cyrus Shahabi · 2005
Due to the information explosion, a growing number of applications store, maintain, and retrieve large volumes of data, where the data is required to be available online or near-online. These data repositories are implemented using hierarchical storage structures (HSS). One of the components of HSS is tertiary storage, which provides cost-effective storage for the vast amount of data manipulated by these applications. However it is crucial that the 3-4 orders of magnitude difference in access time between tertiary storage and secondary storage be bridged to allow online or near-online access to the tertiary resident data. This wide access-gap is mainly due to: the sequential nature of the most popular tertiary technologies (i.e., tapes) and the low number of drives per media in tertiary storage jukeboxes. In this paper we propose a novel data placement technique specifically designed for the serpentine tape technology, namely: wrap around data placement (WARP). We focus on tape technology because it provides the most cost-effective storage for very large databases, and more specifically on serpentine tapes because they are increasingly the technology of choice for mid-range and high-end systems. WARP may reduce the access time by 1 order of magnitude, depending on the tape device specifications and object sizes. An important feature of WARP is that it optimizes access-time independently of the retrieval order. This is achieved by exploiting the serpentine tape technology characteristics as opposed to the application characteristics.