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BACTAC - Morrey and Aiken

Research Talks
Graduate Student, Department of Computer Science
Stephen Aiken
Graduate Student, Department of Computer Science
4/1/2003
3:30pm-4:30pm
Brad Morrey -- The Peabody Network Block Storage Device

Disk drives are now available with capacities on the order of hundreds of gigabytes. What has not become available is an easy way to manage storage. With installed machines located across the enterprise, the backup, management of application installation, and maintenance of systems have become a nightmare. An increasing trend in the storage industry is to virtualize storage resources, maintaining a central repository that can be accessed across the network. We have designed a network block storage device, Peabody, that exposes virtual disks. These virtual disks provide mechanisms to: recover any previous state of their sectors and share backend storage to improve cache utilization and reduce the total amount of storage needed.

Peabody is exposed as an iSCSI target, and is mountable by any iSCSI compatible initiator. Using our implementation of Peabody, we show that for our workloads, up to 84% of disk sectors written contain identical content to previously written sectors, motivating the need for content-based coalescing. The overhead for writing in a simple implementation is only 20 percent of the total write speed.

This paper describes our early experiences with the Peabody implementation. We quantify how rapidly storage is consumed, examine optimizations, such as content-based coalescing and describe how recovery is currently implemented. We conclude with future plans based on these measurements.

Steven Aiken -- Performance of iSCSI Protocol

Fibre channel has long dominated the realm of storage area networks (SAN's). However, with increased development and refining, iSCSI is fast becoming an equal contender, which is causing many companies to reconsider how future storage networks shall be implemented. In addition to reduced costs and a unified network infrastructure, iSCSI allows for the deployment of storage networks over a commodity internet. Moreover, there are inexpensive software implementations of the iSCSI protocol that may provide compelling platforms for iSCSI deployment.

This paper discusses findings of a performance study on the iSCSI protocol in four different configurations. The first two consist of iSCSI in a more commercial setting, where specialized hardware is used for the iSCSI target and two different configurations are examined for the initiator. These results are contrasted with the performance of fibre channel in a similar setting. The second two configurations focus on iSCSI deployed purely in software in both SAN and WAN environments. The performance results indicate that the iSCSI protocol can be severely limited by the implementation. This is due to either inefficient handling of the underlying network, or to not using sufficient system resources to take advantage of a network.

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University of Colorado Boulder
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