Toshihiro Nemoto

Simulation Studies of the Cassette Migration Activities in a Scalable Tape Archiver

With the prolifemtion of multimedia applications, even secondary storage systems do not have sufficient storage capacity to meet the demand, only tertiary storage systems can provide the necessary storage economically. We have been examining the feasibility of “‘scalable tape archiver” where any number of commodity 8mm based robotics can be connected to allow the development of arbitrary sized archives economically. 8mm tape based robotics which can mechanically exchange cassette tapes through a special transportation port were designed and built. By migrating the frequently accessed, HOT, cassettes evenly amongst the archivers in both the foreground and background, we can improve the performance of the system significantly compared with systems without the ability to migrate cassettes. In this paper, we analyze the migration activities on scalable tape archiver. When heat imbalance is detected, migration activities are invoked, which we examined in detail through simulations using the parameters taken from the real archivers. The case where a file is striped over several tapes is also carefully examined. In addition, in our system, even when some of the drives fail, the system can continue unaffected by dynamically migrating the cassettes to the archivers which have working drives. We examined the migration activities when drive failure occurs. Our simulation study clari..ed the eflectiveneas of the scalable tape archiver.

Performance evaluation of cassette migration mechanism for scalable tape archiver

Recent attention on global environmental changes has stimulated the development of large scale global information systems. Satellite images play a very important role for understanding these global changes, but their data size are very large. Magnetic tape archivers are often used for them because of their capacity, but their capacity cannot be increased except by adding a new archiver which is independent of the others. We designed a scalable tape archiver, which consists of several element archivers and can be extended to any number of archivers. Each element archiver can transfer a cassette to a neighboring one. In the scalable tape archiver, performance strongly depends on data placement and usage of the tape drives. In this paper, we propose several cassette tape migration algorithms to balance the load across the element archivers and also evaluate the performance of the various proposed algorithms through simulation.

Partial migration in an 8mm tape based tertiary storage file system and its performance evaluation through satellite image processing applications

Recent attention on global environmental changes has stimulated the development of large scale global information systems. Satellite images play a very important role for understanding these global changes. However, the data size is very large and current commercial hierarchical file management systems are not efficient enough to handle such huge data files. Migration of a whole file from tape to disk takes a very long time. Usually users are not interested in a whole image but in only a small portion of it. Thus, there is no need for full migration.

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 Earths 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.

Surveying Systems of Global Climate Change Simulation Data and Access Logs to Them

This paper introduces the browser for multi-dimensional dataset such as global climate change simulation datasets and the visualization system for access logs to the datasets which we are now constructing. Many of large scientific datasets have multi-dimensional structures and it is necessary to consider multi-dimension to browse such datasets in order to utilize the data efficiently and to understand the behavior of the requests for them.

Load balancing algorithm using tape migration mechanisms for scalable tape archiver and its performance evaluation

In this paper the authors describe a load balancing algorithm and its validity in a scalable tape archiver consisting of a small-scale tape archiver used as a single element and a tape migration device connected to these elements which enables the physical transfer of tapes. With the rapid development of small-scale archivers for multimedia applications in recent years, such archivers are expected to become commercial products in the near future. By connecting an arbitrary number of such inexpensive element archivers together, an archiver system of the desired scale can be created in a flexible and cost-efficient fashion. In this paper the authors describe their load balancing algorithm for use among the element archivers and then demonstrate its validity through simulations. By balancing any biases in the access frequency through the use of the tape migration mechanism, the authors show that considerable performance improvements can be obtained. In addition, they also show that the tape migration mechanism is useful for tape drive failures, as well as demonstrating that performance improvements can be obtained even when using file striping. Finally, the authors perform simulations using the access history for a satellite image database and show that the tape migration mechanism is useful for real-world applications as well.

Implementation of tertiary storage file system with partial migration mechanism on an 8 mm tape archiver and its performance evaluation

Recently the demand for large-scale file systems has been increasing for global information systems, multimedia databases and so on. However, current commercial hierarchical file management systems are not efficient enough to handle huge data files. Migration of a whole file from a tape to a disk takes a very long time. Usually, users are not interested in a whole image but only in a small portion of it. Thus, there is no need for full migration. We designed and implemented a partially migratable file system based on 8 mm tape archivers. The file system transfers only the necessary portion of a file onto the disk. Two real application programs, radiometric/geometric correction and NDVI (Normalized Difference Vegetation Index) generation, were chosen and executed using our experimental file system. Large performance improvements were achieved compared to the conventional file-level migration scheme.