文档介绍：Google puting Faculty Training Workshop
Module VI: Distributed Filesystems
This presentation includes course content © University of Washington
Some slides designed by Alex Moschuk, University of Washington
Redistributed under the mons Attribution license
All the rest:
© Spinnaker Labs, Inc.
Outline
Filesystems overview
NFS & AFS (Andrew File System)
GFS
© Spinnaker Labs, Inc.
File Systems Overview
System that permanently stores data
Usually layered on top of a lower-level physical storage medium
Divided into logical units called “files”
Addressable by a filename (“”)
Usually supports hierarchical nesting (directories)
File Paths
A file path joins file & directory names into a relative or absolute address to identify a file
Absolute: /home/aaron/
Relative: docs/
The shortest absolute path to a file is called its canonical path
The set of all canonical paths establishes the namespace for the filesystem
© Spinnaker Labs, Inc.
What Gets Stored
User data itself is the bulk of the file system's contents
Also includes meta-data on a drive-wide and per-file basis:
Drive-wide:
Available space
Formatting info
character set
...
Per-file:
name
owner
modification date
physical layout...
High-anization
Files anized in a “tree” structure made of nested directories
One directory acts as the “root”
“links”(symlinks, shortcuts, etc) provide simple means of providing multiple access paths to one file
Other file systems can be “mounted” and dropped in as sub-hierarchies (other drives, network shares)
Low-anization (1/2)
File data and meta-data stored separately
File descriptors + meta-data stored in inodes
Large tree or table at designated location on disk
Tells how to look up file contents
Meta-data may be replicated to increase system reliability
Low-anization (2/2)
“Standard” read-write medium is a hard drive (other media: CDROM, tape, ...)
Viewed as a sequential array of blocks
Must address ~1 KB chunk at a time
Tree structure i