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Operating System Concepts (16)

Module 16: Distributed-System Structures. • Network-Operating Systems. • Distributed-Operating Systems. • Remote Services. • Robustness. • Design Issues. 16.1 Silberschatz and Galvin 1998 Network-Operating Systems.• Users are aware of multiplicity of machines. Access to. resources of various machines is done explicitly by:. – Remote logging into the appropriate remote machine – Transferring data from remote machines to local. machines, via the File Transfer Protocol (FTP). mechanism 16.2 Silberschatz and Galvin 1998 Distributed-Operating Systems.• Users not aware of multiplicity of machines. Access to remote. resources similar to access to local resources• Data Migration – transfer data by transferring entire file, or. transferring only those portions of the file necessary for the. immediate task• Computation Migration – transfer the computation, rather than. the data, across the system 16.3 Silberschatz and Galvin 1998 Distributed-Operating Systems (Cont.).• Process Migration – execute an entire process, or parts of it, at. different sites – Load balancing – distribute processes across netowrk to. even the workload – Computation speedup – subprocesses can run. concurrently on different sites – Hardware preference – process execution may require. specialized processor – Software preference – required software may be available. at only a particular site – Data access – run process remotely, rather than transfer. all data locally 16.4 Silberschatz and Galvin 1998 Remote Services• Requests for access to a remote file are delivered to the. server. Access requests are translated to messages for the. server, and the server replies are packed as messages and. sent back to the user• A common way to achieve this is via the Remote Procedure. Call (RPC) paradigm• Messages addressed t an RPC daemon listening to a port on. the remote system contain the name of a process to run and. the parameters to pass to the process. The process is. executed as requested, and any output is sent back to the. requester in a separate message• A port is a number included at the start of a message packet A system can have many ports within its one network address. to differentiate the network services it supports. 16.5 Silberschatz and Galvin 1998 RPC Scheme Binds Client and Server Port.• Binding information may be predecided, in the form of fixed. port addresses – At compile time, an RPC call has a fixed port number. associated with it – Once a program is complied, the server cannot change. the port number of the requested service• Binding can be done dynamically by a rendezvous mechanism – Operating system provides a rendezvous daemon on a. fixed RPC port – Client then sends a message to the rendezvous daemon. requesting the port address of the RPC it needs to. execute 16.6 Silberschatz and Galvin 1998 RPC Scheme (Cont.).• A distributed file system (DFS) can be implemented as a set of. RPC daemons and clients – The messages are addressed to the DFS port on a server. on which a file operation is to take place – The message contains the disk operation to be performed. (i.e., read, write, rename, delete or status) – The return message contains any data resulting from that. call, which is executed by the DFS daemon on behal