1). Replicated file system: a simple way to increase the likelihood that a critical data file is always accessible is to keep a back-up copy of the file on another disk, usually one that is attached to a different machine. The file system provides transparent replication. In particular, suppose there are n copies of a data file and n server modules. Each server provides access to one copy of the file. A client interacts with any one of the server modules. The servers interact with each other to present clients with the illusion that there is a single copy of the file. Each file exports four operations: open, close, read and write for client. The file servers interact with each other to ensure that copies of the file are kept consistent and that at most one client at a time is permitted to write into the file. Each file servers has a local lock manager process that implements a solution to the readers/writer problem. Some points to bear in mind:

a. Each fileserver exports two sets of operations: those called by its clients and those called by other fileservers. Each server module keeps track of current access mode by using a lock manager. For example, the file is not written if it is opened for reading. Multiple readings however are allowed. If a certain operation needs to get permission from all lock managers, please acquire the locks in the same order for all clients. Otherwise, deadlock may occur.

b. Within write procedure, a module first update its local copy then concurrently updates every remote copy. It is analogous to using a write-through cache update policy. An alternative approach would be to update the remote copy when the file is closed.

Demo purpose: Store duplicated simple text files in several fileservers for demo purpose. Write operation just simply appends more text to the file. Client gets connected to any fileserver in a graphical user interface.

Habilidades: Java

Veja mais: problem of points solution, policy writer, operation manager, c# read and write text file, operation not permitted, remote writer, illusion, deadlock, copy file system system java, java local file, copy file server using java, file cache, copy file java, using java simple file server, copy file server java, java file manager, process file java, simple file replication, simple system using java, file open process, java client server multiple, java client server example, java system using access, open text file java, writer policy

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