No description available.

No description available.

No description available.

No description available.

No description available.

Modern distributed applications often have to make a choice about how to main- tain data within the system. Distributed storage systems are often self- contained in a single cluster or are a black box as data placement is unknown by an applica- tion. Using wide area distributed storage either means using multiple APIs or loss of control of data placement. This work introduces Sage, a distributed filesystem that aggregates multiple backends under a common API. It also gives applications the ability to decide where file data is stored in the aggregation. By leveraging Sage, users can create applications using multiple distributed backends with the same API, and still decide where to physically store any given file. Sage uses a layered design where API calls are translated into the appropriate set of backend calls then sent to the correct physical backend. This way Sage can hold many backends at once mak- ing them appear as the same filesystem. The performance overhead of using Sage is shown to be minimal over directly using the backend stores, and Sage is also shown to scale with respect to backends used. A case study shows file placement in action and how applications can take advantage of the feature. / Graduate

No description available.

The problem of distributed state estimation over a sensor network in which a set of nodes collaboratively estimates the state of continuous-time linear systems is considered. Distributed estimation strategies improve estimation and robustness of the sensors to environmental obstacles and sensor failures in a sensor network. In particular, this dissertation focuses on the benefits of weight adaptation of the interconnection gains in distributed Kalman filters, distributed unknown input observers, and distributed functional observers. To this end, an adaptation strategy is proposed with the adaptive laws derived via a Lyapunov-redesign approach. The justification for the gain adaptation stems from a desire to adapt the pairwise difference of estimates as a function of their agreement, thereby enforcing an interconnection-dependent gain. In the proposed scheme, an adaptive gain for each pairwise difference of the interconnection terms is used in order to address edge-dependent differences in the estimates. Accounting for node-specific differences, a special case of the scheme is presented where it uses a single adaptive gain in each node estimate and which uniformly penalizes all pairwise differences of estimates in the interconnection term. In the case of distributed Kalman filters, the filter gains can be designed either by standard Kalman or Luenberger observers to construct the adaptive distributed Kalman filter or adaptive distributed Luenberger observer. Stability of the schemes has been shown and it is independent of the graph topology and therefore the schemes are applicable to both directed and undirected graphs. The proposed algorithms offer a significant reduction in communication costs associated with information flow by the nodes compared to other distributed Kalman filters. Finally, numerical studies are presented to illustrate the performance and effectiveness of the proposed adaptive distributed Kalman filters, adaptive distributed unknown input observers, and adaptive distributed functional observers.

- english version ZlomekFS is a distributed filesystem which is able to share data among nodes. These nodes can cooperate in various modes. Modes differ in caching of local data at the client side and in the way how data is synchronized between the client and the server. This synchronization has been implemented by an unsecured and untrusted network connection until now. The current implementation uses FUSE interface for the communication between the kernel of the filesystem and the user. The synchronization is triggered when the user performs a specific operation above the filesystem. For well functionality in modern network environment it is necessary to both communicating partners to be sure about the identity of the second end of a communicating channel. This thesis implements trustworthy connection between the server and the client part of filesystem. In addition, it separates machine and user type of client. Next important part of the thesis is correct data synchronization and precise definition of sharing semantics.

Distributed file systems have become popular because they allow information to be shared be between computers in a natural way. A distributed file system often forms a central building block in a distributed system. Currently most distributed file systems are built using a communications interface that transfers messages about files between machines. This thesis proposes a different, lower level, communications interface. This `block-based' interface exchanges information about the blocks that make up the file but not about the files themselves. No other distributed file system is built this way. By demonstrating that a distributed file system can be implemented in a block-based manner, this thesis opens the way for many advances in distributed file systems. These include a reduction of the processing required at the server, uniformity in managing file blocks and fine-grained placement and replication of data. The simple communications model also lends itself to efficient implementation both at the server and in the communications protocols that support the interface. These advantages come at the cost of a more complex client implementation and the need for a lower level consistency mechanism. A block-based distributed file system (BB-NFS) has been implemented. BB-NFS provides the Unix file system interface and demonstrates the feasibility and implementability of the block-based approach. Experience with the implementation lead to the development of a lock cache mechanism which gives a large improvement in the performance of the prototype. Although it has not been directly measured it is plausible that the prototype will perform better than the file based approach. The block-based approach has much to offer future distributed file system developers. This thesis introduces the approach and its advantages, demonstrates its feasibility and shows that it can be implemented in a way that performs well.