NASD: Cheops Overview

Network-attached secure disks (NASDs) exploit switched networks to offer scalable storage by moving the file server off the storage access path, reducing its function to an off-line, name-mapping access authorization service, allowing clients to directly access NASD devices. Traditionally, network shared services and abstractions are provided by layering services on shared machines (e.g. a web server above a file server above a RAID controller) with each server inducing a store-and-forward data copy and a synchronous serialization point. While this type of layering simplifies implementation because of centralized state, it creates a performance and scalability bottleneck and adds substantial cost to the system.

Research on Cheops focuses on the problem of providing an enhanced storage service on top of NASDs offering RAID, storage migration and load balanced allocation without reintroducing synchronous shared servers.

The focus of the research is to investigate the architecture, protocols and the NASD support required to enable such decentralized scalable operation. In particular, the goal is to define and implement NASD support, thus enabling scalable storage service (in particular scalable synchronization), as well as algorithms to provide object migration, allocation, and load balancing with high scalability.

Overview of function decomposition in Cheops/Nasd

This figure contrasts a traditional layered model where client requests travel through a stack of abstractions implemented at the server machine (a) to a decomposed model in the Cheops/NASD where clients implement most of the resource intensive operations locally (at the local storage clerk) (b).

Cheops involves clients in the implementation of enhanced storage abstractions to ensure scalability. However, by virtue of its design, client involvement in Cheops does not compromise security. Furthermore, to achieve true scalability, Cheops does not require global synchronization protocols across clients.

For instance, synchronization is distributed so that there is no single synchronization point. Instead, the NASD that stores the data handles the synchronization concerning that data. Clients operate in a loosely coupled fashion, and synchronize optimistically at the NASD drive when they access the data.

Current Results

So far, the following areas in Cheops are showing promising results:






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Last updated 12 March, 2012