Module 23 Fancy File Systems

NFS

network file system, where files are stored on a remote file server, client accesses files transparently

RPC

clients execute services on a remote server using a procedure call

RPC lower level

mechanism that generates client stubs and server stubs that are used for communicating messages for procedure call

consistency models

shared data that is kept in a data store that clients can access the data through read and write operations

coherence

resitricts order of reads and writes to one location

staleness

bounds maximum ( real time ) delay between writes and reads to one location

Consistency

restricts orders of reads and writes across locations

sequential consistency

create a total order that includes all the operations of the execution

FIFO Consistency

Writes done by a single process are seen by all

other processes in the order in which they

were issued, but writes from different

processes may be seen in a different order by

different processes”

Causal Consistency

Writes that are potentially causally related must

be seen by all processes in the same order.

Concurrent writes may be seen in a different

order on different machines

stateless protocol

server maintains no state about clients or open files

idempotent operations

all requests can be repeated

GFS

file system optimized for very large files with particular access patterns and for a very large number of simultaneous clients