Lecture 15 Network file systems

Lecture 15 Network file systems - Administrivia Project 3...

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Unformatted text preview: Administrivia Project 3 due now But because you are here, you can turn it in any time up to today- Put in your design doc- Or state all team members are SCPD students If you need longer, email cs140-staff Remember Friday section on Project 4 1/37 Network file systems Whats a network file system?- Looks like a file system (e.g., FFS) to applications- But data potentially stored on another machine- Reads and writes must go over the network- Also called distributed file systems Advantages of network file systems- Easy to share if files available on multiple machines- Often easier to administer servers than clients- Access way more data that fits on your local disk- Network + remote buffer cache faster than local disk Disadvantages- Network + remote disk slower than local disk- Network or server may fail even when client OK- Complexity, security issues 2/37 Naming structures Location transparency file name does not reveal the files physical storage location- File name still denotes a specific, although hidden, set of physical disk blocks- Convenient way to share data- Can expose correspondence between component units and machines Location independence file name need not change when the files physical storage location changes- Better file abstraction- Promotes sharing the storage space itself- Separates the naming hierarchy form the storage-devices hierarchy 3/37 Naming schemes File names include server and local path (URLs)- E.g., http://server.stanford.edu/home/dm unique name- Variation: Include cryptographically secure name for server Attach remote directories to local directories (NFS)- Gives appearance of a coherent directory tree- Only previously mounted remote directories accessible Total integration of the component file systems (AFS)- A single global name structure spans all the files in the system- If a server is unavailable, some arbitrary set of directories on different machines also becomes unavailable Name by the data you want ( Chord CFS , IVY )- Very non-standard administrative model (impractical?)- Some big advantages like scalability & fault tolerance 4/37 NFS version 2 [Sandberg] Background: ND (networked disk)- Creates disk-like device even on diskless workstations- Can create a regular (e.g., FFS) file system on it- But no sharing (FFS doesnt know how to share disk) Some Goals of NFS- Maintain Unix semantics- Crash recovery- Competitive performance with ND 5/37 NFS implementation Virtualized the file system with vnodes- Basically poor mans C++ (like protosw struct) Vnode structure represents an open (or openable) file Bunch of generic vnode operations:- lookup, create, open, close, getattr, setattr, read, write, fsync, remove, link, rename, mkdir, rmdir, symlink, readdir, readlink, ......
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Lecture 15 Network file systems - Administrivia Project 3...

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