Khalil Amiri

A cost-effective, high-bandwidth storage architecture

This paper describes the Network-Attached Secure Disk (NASD) storage architecture, prototype implementations oj NASD drives, array management for our architecture, and three, filesystems built on our prototype. NASD provides scalable storage bandwidth without the cost of servers used primarily, for transferring data from peripheral networks (e.g. SCSI) to client networks (e.g. ethernet). Increasing datuset sizes, new attachment technologies, the convergence of peripheral and interprocessor switched networks, and the increased availability of on-drive transistors motivate and enable this new architecture. NASD is based on four main principles: direct transfer to clients, secure interfaces via cryptographic support, asynchronous non-critical-path oversight, and variably-sized data objects. Measurements of our prototype system show that these services can be cost-effectively integrated into a next generation disk drive ASK. End-to-end measurements of our prototype drive andfilesysterns suggest that NASD cun support conventional distributed filesystems without performance degradation. More importantly, we show scaluble bandwidth for NASD-specialized filesystems. Using a parallel data mining application, NASD drives deliver u linear scaling of 6.2 MB/s per clientdrive pair, tested with up to eight pairs in our lab.

File server scaling with network-attached secure disks

By providing direct data transfer between storage and client, network-attached storage devices have the potential to improve scalability for existing distributed file systems (by removing the server as a bottleneck) and bandwidth for new parallel and distributed file systems (through network striping and more efficient data paths). Together, these advantages influence a large enough fraction of the storage market to make commodity network-attached storage feasible. Realizing the technologys full potential requires careful consideration across a wide range of file system, networking and security issues. This paper contrasts two network-attached storage architectures---(1) Networked SCSI disks (NetSCSI) are network-attached storage devices with minimal changes from the familiar SCSI interface, while (2) Network-Attached Secure Disks (NASD) are drives that support independent client access to drive object services. To estimate the potential performance benefits of these architectures, we develop an analytic model and perform trace-driven replay experiments based on AFS and NFS traces. Our results suggest that NetSCSI can reduce file server load during a burst of NFS or AFS activity by about 30%. With the NASD architecture, server load (during burst activity) can be reduced by a factor of up to five for AFS and up to ten for NFS.

Highly concurrent shared storage

Switched system-area networks enable thousands of storage devices to be shared and directly accessed by end hosts, promising databases and file systems highly scalable, reliable storage. In such systems, hosts perform access tasks (read and write) and management tasks (storage migration and reconstruction of data on failed devices.) Each task translates into multiple phases of low-level device I/Os, so that concurrent host tasks accessing shared devices can corrupt redundancy codes and cause hosts to read inconsistent data. Concurrent control protocols that scale to large system sizes are required in order to coordinate on-line storage management and access tasks. In this paper we identify, the tasks that storage controllers must perform, and propose an approach which allows these tasks to be composed from basic operations-called base storage transactions (BSTs)-such that correctness requires only the serializability of the BSTs and not of the parent tasks. We present highly scalable distributed protocols which exploit storage technology trends and BST properties to achieve serializability while coming within a few percent of ideal performance.