Scalable tape archiver for satellite image database and its performance analysis with access logs. Hot declustering and hot replication

Recently, global environmental studies have become very important around the world. Repeated observations of wide areas of the earth at the same time makes satellite images useful. For understanding Earth's environment it is necessary to use a substantial amount of the temporally sequenced satellite images. At the Institute of Industrial Science, University of Tokyo, we have been building a global environmental digital library whose main contents are earth surface images from NOAA environmental satellite images and GMS images received at our institute. In this paper, we describe our satellite image archive system. We focus on a scalable tape archiver (STA), which is a key component of our archive system. We explain two orthogonal file/cassette replacement strategies, declustering and replicating, adopted for the STA and show their effectiveness. After their basic performance is shown, we describe a performance analysis using access traces taken at our archive system. The proposed schemes named hot declustering and hot replication, work effectively in our STA in daily operations.