Multiple Processor SystemsMultiprocessor SystemsMultiprocessor Hardware (2)Multiprocessor Hardware (3)Multiprocessor Hardware (4)Multiprocessor OS Types (1)Multiprocessor OS Types (2)Multiprocessor OS Types (3)MulticomputersMulticomputer Hardware (1)Remote Procedure Call (1)Distributed Systems (1)Document-Based MiddlewareFile System-Based Middleware (1)File System-Based Middleware (2)Network File SystemNFS architectureNFS Architecture (contd.)NFS ProtocolMountingFile AccessImplementationVnode useRemote File AccessMultiple Processor SystemsChapter 88.1 Multiprocessors 8.2 Multicomputers 8.3 Distributed systemsMultiprocessor SystemsContinuous need for faster computersshared memory modelmessage passing multiprocessorwide area distributed systemMultiprocessor Hardware (2)UMA Multiprocessor using a crossbar switchMultiprocessor Hardware (3)Multiprocessors using multistage switching networks can be built from 2x2 switches (a) 2x2 switch (b) Message formatMultiprocessor Hardware (4)Omega Switching NetworkMultiprocessor OS Types (1)Each CPU has its own operating systemBusMultiprocessor OS Types (2)Master-Slave multiprocessorsBusMultiprocessor OS Types (3)Symmetric MultiprocessorsSMP multiprocessor modelBusMulticomputersDefinition:Tightly-coupled CPUs that do not share memoryAlso known as cluster computersclusters of workstations (COWs)Multicomputer Hardware (1)Interconnection topologies(a) single switch(b) ring(c) grid(d) double torus(e) cube(f) hypercubeRemote Procedure Call (1)Steps in making a remote procedure callthe stubs are shaded grayDistributed Systems (1)Achieving uniformity with middlewareDocument-Based Middleware How the browser gets a page1. Asks DNS for IP address2. DNS replies with IP address3. Browser makes connection 4. Sends request for specified page5. Server sends file6. TCP connection released7. Browser displays text8. Browser fetches, displays imagesFile System-Based Middleware (1)Transfer Models(a) upload/download model(b) remote access model(a)(b)File System-Based Middleware (2)Naming Transparency(b) Clients have same view of file system(c) Alternatively, clients with different view01/14/19 BR 16Network File System The Network File System (NFS) was developed to allow machines to mount a disk partition on a remote machine as if it were on a local hard drive. This allows for fast, seamless sharing of files across a network. Three aspects of NFS are of interest: the architecture, the protocol, and the implementation.01/14/19 BR 17NFS architectureUNIX kernelprotocolClient computer Server computersystem callsLocal RemoteUNIXfilesystemNFSclientNFSserverUNIXfilesystemApplicationprogramApplicationprogramNFSUNIXUNIX kernelVirtual file systemVirtual file systemOther file system01/14/19 BR 18NFS Architecture (contd.)Allows an arbitrary collection of clients and servers to share a common file system.In many cases all servers and clients are on the same LAN but this is not required.NFS allows every machine to be a client and server at the same time.Each NFS server exports one or more directories for access by remote clients.01/14/19 BR 19NFS ProtocolOne of the goals o NFS is to support a heterogeneous system, with clients and servers running different operating systems on different hardware. It is essential the interface between clients and server be well defined.NFS accomplishes this goal by defining two client-server protocol: one for handling mounting and another for directory and file access.Protocol defines requests by clients and responses by servers.01/14/19 BR 20MountingClient requests a directory structure to be mounted, if the path is legal the server returns file handle to the client.Or the mounting can be automatic by placing the directories to mounted in the /etc/rc: automounting.01/14/19 BR 21File AccessNFS supports most unix operations except open and close. This is to satisfy the “statelessness” on the server end. Server need not keep a list of open connections. See the operations listed in earlier slides.(On the other hand consider your database connection… you create an object, connection is opened etc.)01/14/19 BR 22ImplementationAfter the usual system call layer, NFS specific layer Virtual File System (VFS) maintains an entry per file called vnode (virtual I-node) for every open file.Vnode indicate whether a file is local or remote.For remote files extra info is provided.For local file, file system and I-node are specified.Lets see how to use v-nodes using a mount, open, read system calls from a client application.01/14/19 BR 23Vnode useTo mount a remote file system, the sys admin (or /etc/rc) calls the mount program specifying the remote directory, local directory in which to be mounted, and other info.If the remote directory exist and is available for mounting, mount system call is made.Kernel constructs vnode for the remote directory and asks the NFS-client code to create a r-node (remote I-node) in its internal tables. V-node in the client VFS will point to local I-node or this r-node.01/14/19 BR 24Remote File AccessWhen a remote file is opened by the client, it locates the r-node.It then asks NFS Client to open the file. NFS file looks up the path in the remote file system and return the file handle to VFS tables.The caller (application) is given a file descriptor for the remote file. No table entries are made on the server side.Subsequent reads will invoke the remote file, and for efficiency sake the transfers are usually in large chunks
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