Alain Azagury

Combining card marking with remembered sets: how to save scanning time

We consider the combination of card marking with remembered sets for generational garbage collection as suggested by Hosking and Hudson [3]. When more than two generations are used, a naive implementation may cause excessive and wasteful scanning of the cards and thus increase the collection time. We offer a simple data structure and a corresponding algorithm to keep track of which cards need be scanned for which generation. We then extend these ideas for the Train Algorithm of [4]. Here, the solution is more involved, and allows tracking of which card should be scanned for which car-collection in the train.

A two layered approach for securing an object store network

Storage Area Networks (SAN) are based on direct interaction between clients and storage servers. This unmediated access exposes the storage server to network attacks, necessitating a verification, by the server, that the client requests conform with the system protection policy. Solutions today can only enforce access control at the granularity of entire storage servers. This is an outcome of the way storage servers abstract storage: an array of fixed size blocks. Providing access control at the granularity of blocks is infeasible there are too many active blocks in the server of entire servers is used. Object, stores (e.g, the NASD system) on the other hand provide means to address these issues. An object store control unit presents an abstraction of a dynamic collection of objects, each can be seen as a different array of blocks, thus providing the basis for Protection at the object level. In this paper we present a security model for the object store which leverages on existing security infrastructure. We give a simple generic mechanism capable of enforcing an arbitrary access control policy at object granularity. This mechanism is specifically designed to achieve low overhead by minimizing the cost of validating an operation along the critical data path, and lends itself for optimizations such as caching The key idea of the model is to separate the mechanisms for transport security from the one used for access control and to maximize the use standard security protocols when possible We utilize a standard industry protocol for authentication, integrity and privacy on the communication channel (IPSec for IP networks) anti fine a proprietary protocol for authorization on top of the secure communication layer.

IBM research division cloud computing initiative

Cloud computing represents the latest phase in the evolution of Internet-based computing. In this paper, we describe the fundamental building blocks of cloud computing and the initiative undertaken by the IBM Research Division in this area, which includes work on Internet-scale data centers, virtualization, scalable storage, and cloud computing services. The focus of this project has been the Research Compute Cloud, an environment for cloud computing research that is also used as a computing resource by various groups in the IBM Research Division.

A novel navigation paradigm for XML repositories

The advances in storage and communications enable users to store massive amounts of data, and to share it seamlessly with their peers. With the advent of XML, we expect a significant portion of this data to be in XML format. We describe here the architecture and implementation of an XML repository that promotes a novel navigation paradigm for XML documents based on content and context. Support for these capabilities is achieved by bringing to bear the organizational power of information retrieval to the domain of semistructured documents. File systems remain the preferred storage infrastructure for the home and business desktop environments. We have built a system, XMLFS, based on the ideas stated above. XMLFS presents a storage abstraction that manifests itself to the client as a familiar file system. However, it breaks the tight coupling between the directory hierarchical structure and the file system. XMLFS creates automatically a directory organization of any XML document collection based on content and context. Each user can navigate through the file system according to her/his domain of interest at that point in time. Our result is a first step towards a solution to the discovery and navigation problems presented by the collective repositories of XML documents in peer-to-peer environments.

Highly available cluster: a case study

The methodology and design of a system that provides highly available data in a cluster is presented. A highly available cluster consists of multiple machines interconnected by a common bus. Data is replicated at a primary and one or more backup machines. Data is accessed at the primary, using a location independent mechanism that ensures data integrity. If the primary copy of the data fails, access is recovered by switching to a backup copy. Switchover is transparent to the application, hence called seamless switchover. The fault model is fail-stop. The entire cluster is resilient to at least single failures. Designating data as highly available is selective in scope, and the overhead of replication and recovery is incurred only by applications that access highly available data. An experimental prototype was implemented using IBM AS/400 machines and a high-speed bus with fiber-optic links.<<ETX>>

A note on the implementation of replication-based garbage collection for multithreaded applications and multiprocessor environments

Replication-based incremental garbage collection is one of the more appealing concurrent garbage collection algorithms known today. It allows continuous operation of the application (the mutator) with very short pauses for garbage collection. There is a growing need for such garbage collectors suitable for a multithreaded environments such as the Java Virtual Machine. Furthermore, it is desirable to construct collectors that also work on multiprocessor computers. We begin by pointing out an important, yet subtle point, which arises when implementing the replication-based garbage collector for a multithreaded environment. We first show that a simple and natural implementation of the algorithm may lead to an incorrect behavior of multithreaded applications. We then show that another simple and natural implementation eliminates the problem completely. Thus, the contribution of this part is in stressing this warning to future implementors. Next, we address the effects of the memory coherence model on this algorithm. We show that even when the algorithm is properly implemented with respect to our first observation, a problem might still arise when a multiprocessor system is used. Adopting a naive solution to this problem results in very frequent (and expensive) synchronization. We offer a slight modification to the algorithm which eliminates the problem and requires little synchronization.

GPFS-based implementation of a hyperconverged system for software defined infrastructure

The need for an increasingly dynamic and more cost-efficient data-center infrastructure has led to the adoption of a software defined model that is characterized by: the creation of a federated control plane to judiciously allocate and control appropriate heterogeneous infrastructure resources in an automated fashion, the ability for applications to specify criteria, such as performance, capacity, and service levels, without detailed knowledge of the underlying infrastructure; and the migration of data-plane capabilities previously embodied as purpose-built devices or firmware into software running on a standard operating systems in commercial off-the-shelf servers. This last trend of hardware-based capabilities migrating to software is enabling yet another shift to hyperconvergence, which refers to merger of traditionally separate networking, compute, and storage capabilities in integrated system software. This paper examines the convergence of the software defined infrastructure stack, and introduces a hyperconverged compute and storage architecture, in which the IBM General Parallel File System (GPFS®) implements the software defined data plane that dynamically supports workloads ranging from high-I/O virtual desktop infrastructure applications to more compute-oriented analytics applications. The performance and scalability characteristics of this architecture are evaluated with a prototype implementation.