http://en.wikipedia.org/wiki/Network_file_system



Any computer file system that supports sharing of files and other resources as persistent storage over a computer network

First file servers were developed in the 1970s,

In 1985 Sun Microsystems created the Network File
System (NFS)

Became the first widely used distributed file system
Other notable distributed file systems

Andrew File System (AFS)

Server Message Block SMB

AKA CIFS

Distribution






Clients, servers, and storage devices
Spread throughout the machines of a distributed system or intranet

System has multiple and independent storage devices
 Some DFS servers run on dedicated machines
 Others a machine can be both a server and a client


As part of a distributed operating system
By a software layer
 Managing the communication between conventional operating systems and file systems

Distribution



Transparency



Multiplicity and dispersion of its servers and storage devices should be invisible

Client interface used by programs should not distinguish between local and remote files
The DFS locates the files and arranges the transport of data

Performance

Most important performance measurement of a
DFS:

Amount of time needed to satisfy service requests

Typical performance constraints:


Conventional systems:


Disk-access time
Small amount of CPU-processing time
DFS:


Additional overhead due to the distributed structure
Includes:
 Time to deliver the request to a server
 Time to deliver the response to the client
 For each direction, a CPU overhead of running the communication protocol software

Performance


Ideally, it would be comparable to that of a conventional file system

Concurrent file updates



Updates to the file from one client should not interfere with access and updates from other clients
Concurrency control or locking may be:


Built into the file system
Provided by an add-on protocol

Sample Network File Systems






9P
Amazon S3
Coda
Secure File System (SFS)
Self-certifying File System (SFS)

Sample Network File Systems

Distributed file systems










Ceph
Andrew File System (AFS), OpenAFS
DCE Distributed File System

Remote file access protocol used with the Distributed Computing Environment
Google File System

File system that is optimized for Google's core storage needs
Hadoop

Java software framework that supports distributed applications running on large clusters of commodity computers
Kosmos FS

High performance distributed file system. It is also integrated with hadoop.
Lustre

Distributed file system for large scale cluster computing
Microsoft Distributed File System

Set of client and server services for organizing many distributed SMB file shares into a distributed file system
GlusterFS

Platform for developing clustering applications
Parallel Virtual File System

Parallel file system that focuses on high performance access to large data sets

http://en.wikipedia.org/wiki/Network_File_System_%28protocol%29




Network file system protocol:

Allows a user on a client computer to access files over a network


As if the network devices were attached to its local disks
Originally developed by Sun Microsystems in 1984
NFS builds on the Open Network Computing
Remote Procedure Call (ONC RPC) system
The Network File System protocol is specified in

RFC 1094, RFC 1813, and RFC 3530 (which obsoletes
RFC 3010)

Versions and variations



Sun used only for in-house experimental purposes
Did not release it to the public

Versions and variations



Originally operated entirely over UDP
Defined in RFC 1094

March 1989

Designers meant to keep the protocol stateless

Locking (for example) implemented outside of the core protocol

Versions and variations


Support for 64-bit file sizes and offsets

Handle files larger than 4 gigabytes (GB)




Support for asynchronous writes on the server

Improve write performance
Additional file attributes in many replies

Avoid the need to re-fetch them
READDIRPLUS operation

Get file handles and attributes along with file names when scanning a directory
Assorted other improvements

Versions and variations



Vendor support for TCP as a transport-layer protocol began increasing
Several vendors had already added support for
NFS Version 2 with TCP as a transport

Sun Microsystems added support for TCP as a transport for NFS at the same time it added support for Version 3

Using TCP as a transport made using NFS over a WAN more feasible

Versions and variations


After Sun Microsystems handed over the development of the NFS protocols

Versions and variations





Performance improvements
Mandates strong security
Introduces a stateful protocol


RFC 3010, December 2000
Revised in RFC 3530, April 2003

Versions and variations



The byte-range advisory Network Lock
Manager (NLM) protocol

Added to support UNIX System V file-locking APIs
The remote quota reporting (RQUOTAD) protocol

Allow NFS-users to view their data-storage quotas on
NFS servers

Versions and variations




Allows NFS to

Integrate more easily into Web-browsers

Enable operation through firewalls
An extension to Version 2 and Version 3
 via https://yanfs.dev.java.net/

Platforms


Other software platforms such can also use the protocol

Mac OS, Microsoft Windows, Novell NetWare, and IBM
AS/400

Platforms




Alternative remote file access protocols include

Server Message Block (SMB, also known as CIFS) protocol



Apple Filing Protocol (AFP)
NetWare Core Protocol (NCP)
OS/400 File Server file system (QFileSvr.400)
SMB and NetWare Core Protocol (NCP) are most common on Microsoft Windows
AFP is most common on Macintosh systems
QFileSvr.400 is most common on AS/400 systems

Typical implementation


Assume a Unix-style scenario: one machine (client) requires access to data stored on another machine (NFS server)






Server implements NFS daemon processes (running by default as nfsd) in order to make its data generically available to clients
Server administrator determines what to make available

Exporting the names and parameters of directories

Typically using the /etc/exports configuration file and the exportfs command
Server security-administration recognizes and approves validated clients
Server network configuration lets appropriate clients can negotiate with it through any firewall system
Client machine requests access to exported data

Issue a mount command
Users on the client machine then view and interact with mounted filesystems on the server within the parameters permitted
Note: automating the NFS mounting process is typical

E.g. using /etc/fstab and/or automounting facilities


1980s

 other.
During the development of the ONC protocol (called SunRPC at the time), only
 whenever two peers shared a common endianness in their machineformed network-computing environments.
Later, Sun and AT&T announced that the two firms would jointly develop AT&T's

System (RFS), and the quick adoption of NFS over RFS by Digital Equipment, HP,
NFS.
OSF solicited the proposals for various technologies, including the remote
Computing Environment (DCE), and the Distributed File System (DFS) won over including NCS and Kerberos . DFS used DCE as the RPC and derived from AFS.



1990s


Sun Microsystems and the Internet Society (ISOC) reached an agreement to cede "change control" of ONC RPC so that ISOC's engineering-standards body, the Internet Engineering Task Force (IETF), could publish standards documents
(RFCs) documenting the ONC RPC protocols and could extend ONC RPC. OSF attempted to make DCE RPC an IETF standard, but ultimately proved unwilling to give up change-control. Later, the IETF chose to extend ONC RPC by adding a new authentication flavor, RPCSEC GSS , in order to meet IETF's requirements that protocol standards have adequate security.
Later, Sun and ISOC reached a similar agreement to give ISOC change control over NFS, although writing the contract carefully to exclude NFS version 2 and version 3. Instead, ISOC gained the right to add new versions to the NFS protocol, which resulted in IETF specifying NFS version 4 in 2003.
2000s

By the 21st century, neither DFS nor AFS had achieved any major commercial success as compared to CIFS or NFS. IBM, which had previously acquired the primary commercial vendor of DFS and AFS, Transarc , donated most of the AFS source code to the free software community in 2000. The OpenAFS project lives on. In early 2005, IBM announced end of sales for AFS and DFS.

Present

NFSv4.1 presents new opportunities for the NAS community

Primary addition is Parallel NFS (pNFS)

A method of introducing data access parallelism




Protocol defines a method of separating the meta-data (names and attributes) of a filesystem from the location of the file data

Goes beyond simple name/data separation

Defines method of striping the data amongst a set of data servers
Very different from the traditional NFS server

Holds the names of files and their data under the single umbrella of the server
Products exist that are multi-node NFS servers

Limited participation by the client in separation of meta-data and data
NFSv4.1 client can be enabled to be a direct participant in the exact location of file data

Avoid sole interaction with the single NFS server when moving data

Present



A collection or community of server resources or components

Community members are controlled by the metadata server

Client moves data to and from the server

Directly interact with the set of data servers belonging to the pNFS server community

Present







Sessions
Directory Delegation and Notifications
Multi-server Namespace
ACL/SACL/DACL
Retention Attributions
SECINFO_NO_NAME

http://en.wikipedia.org/wiki/Andrew_File
_System

(AFS)



Developed by Carnegie Mellon University

Part of the Andrew Project

Named for

Andrew Carnegie

Andrew Mellon

Features

AFS has several benefits over traditional networked file systems




Particularly in the areas of security and scalability
Not uncommon for enterprise AFS cells to exceed fifty thousand clients
Uses Kerberos for authentication

Implements access control lists on directories for users and groups
Each client caches files on the local filesystem for increased speed on subsequent requests for the same file

Allows limited filesystem access in the event of a server crash or a network outage

Features

Read and write operations on an open file are directed only to the locally cached copy





When a modified file is closed

Only the changed portions copied back to the file server
Cache consistency maintained by callback
When a file is cached


Server makes a note of this
Will inform the client if the file is updated by someone else
After any client, server, or network failure (including a time-out)

Callbacks are discarded and must be re-established
Re-establishing a callback involves:


Status check
Does not require re-reading the file itself

Features

Consequence of the whole file locking strategy

AFS does not support large shared databases or record updating within files shared between client systems


Deliberate design decision

Based on the perceived needs of the university computing environment
It leads to the use of a single file per message in the original email system for the Andrew Project, the
Andrew Message System, rather than the more customary single file per mailbox

Features



A significant feature of AFS is the volume



Tree of files
Sub-directories
AFS mountpoints

Links to other AFS volumes
Volumes are created by administrators


Linked at a specific named path in an AFS cell
Once created, users of the filesystem may create directories and files as usual without concern for the physical location of the volume
A volume may have a quota assigned to it in order to limit the amount of space consumed.

As needed, AFS administrators can move that volume to another server and disk location without the need to notify users

Moving can occur while files in that volume are even being used

Features

AFS volumes can be replicated to read-only cloned copies



When accessing files in a read-only volume, a client system will retrieve data from a particular read-only copy
If a copy becomes unavailable, clients will look for any remaining copies


Users of that data are unaware of the location of the readonly copy
Administrators can create and relocate copies as needed
AFS command suite guarantees that all read-only volumes contain exact copies of the original read-write volume at the time the read-only copy was created

Features


Shared name space identical on all workstations

Usually mounted as /afs on the Unix filesystem

Local name space unique to each workstation

Contains only temporary files needed for workstation initialization and symbolic links to files in the shared name space

Features



Heavily influenced Version 4 of Sun
Microsystems' NFS
Variant of AFS adopted by the Open Software
Foundation


Distributed File System (DFS)
Part of their Distributed computing environment

Implementations




There are three major implementations



Transarc (IBM)
OpenAFS
Arla
Transarc software is losing support and is deprecated
AFS (version two) is also the predecessor of the
Coda file system.
A fourth implementation exists in the Linux kernel source code since at least version 2.6.10

Committed by Red Hat



A fairly simple implementation
Still in its early stages of development
Incomplete

Available permissions

The following Access Control List permissions can be granted:

Lookup (l)



 allows a user to list the contents of the AFS directory, examine the ACL associated with the directory and access subdirectories.
Insert (i)
 allows a user to add new files or subdirectories to the directory.
Delete (d)
 allows a user to remove files and subdirectories from the directory.
Administer (a)
 allows a user to change the ACL for the directory. Users always have this right on their home directory, even if they accidentally remove themselves from the ACL.

Available permissions

Permissions that affect files and subdirectories include:



Read (r)
 allows a user to look at the contents of files in a directory and list files in subdirectories. Files that are to be granted read access to any user, including the owner, need to have the standard UNIX "owner read" permission set.
Write (w)
 allows a user to modify files in a directory. Files that are to be granted write access to any user, including the owner, need to have the standard UNIX "owner write" permission set.
Lock (k)
 allows the processor to run programs that need to "flock" files in the directory. See the UNIX man page for "flock" for more details.

Available permissions


http://en.wikipedia.org/wiki/Server_Message_Block

(SMB)



Operates as an application-level network protocol

Applied to shared access to


Files, printers, serial ports, and miscellaneous communications
Between nodes on a network
Provides an authenticated Inter-process communication mechanism
Most usage of SMB involves computers running
Microsoft Windows:

Microsoft environments users often know it simply as
"Microsoft Windows Network"

(SMB)






SMB the protocol
SMB services that run on the protocol
NetBIOS
DCE/RPC services that use SMB as an authenticated Inter-process communication channel (over named pipes)
"Network Neighborhood" protocols which primarily (but not exclusively) run as datagram services directly on the NetBIOS transport

History


Barry Feigenbaum originally invented SMB at IBM

Turn DOS "Interrupt 33" (21h) local file-access into a networked file-system
Microsoft made considerable modifications to the version used most commonly


Merged the SMB protocol with the LAN Manager

Developing with 3Com (circa 1990)
Continued to add features to the protocol


Windows for Workgroups (circa 1992)
Later versions of Windows.

History



Typically implemented with

NBF

NetBIOS over IPX/SPX

NBT
SMB can also run directly on the TCP/IP protocols

Introduced with Windows 2000.

History


About when Sun Microsystems announced
WebNFS


Microsoft launched an initiative in 1996 to rename SMB to
Common Internet File System (CIFS)
Added more features, including


Support for symbolic links, hard links, larger file sizes-and an attempt at supporting direct connections without all the
NetBIOS trimmings
Largely experimental effort that required further refinement
Microsoft submitted some partial specifications as
Internet-Drafts to the IETF

These submissions have expired

History


History



Samba project originated aim of

Reverse engineer SMB

Providing a free implementation of a compatible
SMB-client and server for use with non-Microsoft operating system
Driven by the importance of the SMB protocol in interacting with the widespread Microsoft
Windows platform

Implementation

Client-server approach

SMB works through a peer-to-peer approach



Client makes specific requests and the server responds accordingly
One section of the SMB protocol specifically deals with access to filesystems, such that clients may make requests to a file server

Other sections of the SMB protocol specialize in interprocess communication (IPC)
Developers have optimized the SMB protocol for local subnet usage

Users have also put SMB to work to access different subnets across the Internet
 Involving file-sharing or print-sharing in MS Windows environments

Implementation

Client-server approach

SMB servers make their file systems and other resources available to clients on the network



Client computers may want access to the shared file systems and printers on the server
 For this primary function, SMB is best-known and most heavily used
SMB file-server aspect would count for little without the NT domains suite of protocols
 Provide NT-style domain-based authentication
NT Domains protocols offer MSRPC services available almost exclusively available on SMB IPC "named pipe“
 Almost all implementations of SMB servers use NT Domain authentication to validate user-access to resources

Implementation

Performance issues

Many people believe that the SMB protocol makes heavy use of network bandwidth because each client broadcasts its presence to the whole subnet.







SMB itself does not use broadcasts
 Broadcast problems commonly associated with SMB actually originate with the
NetBIOS service location protocol
Microsoft Windows server will use NetBIOS to advertise and locate services
NetBIOS functions by broadcasting services available on a particular host at regular intervals.
Usually ok for an acceptable default in a network with fewer than 20 hosts
 Broadcast traffic will cause problems as the number of hosts increases.
Proper implementation of a NetBIOS Name Server (NBNS) can mitigate this problem
 Windows Internet Naming Service (WINS) offers a suitable solution in Microsoft environments.
WINS uses a much more advanced system of registration and centralized service requests
 Imposes its own complexity upon the design and maintenance of the network
Microsoft recommends the use of Dynamic DNS
 In Microsoft Active Directory environments

Implementation


Network designers should expect that network latency will have a significant impact on the performance of the SMB protocol

Monitoring reveals this mostly due to navigating among directories through SMB

 When significant network latency exists between hosts
For example, a VPN connection over the Internet will often introduce network latency
 Can make for a frustrating experience

Implementation


Microsoft has added several extensions to its own SMB implementation.


Added NTLM Version 2
 NTLM version 1 used DES in a flawed manner

Derived from the original legacy SMB specification's requirement to use IBM "LanManager" passwords
NT 4.0 Domain Logon protocols use 40-bit encryption outside of the United States of America
 Does not conform with modern security standards

Implementation


SMB's "Inter-Process Communication" mechanism deserves a specific mention

SMB "IPC" system provides named pipes
 Provides one of the first few inter-process mechanisms commonly available to programmers

Provides a means for services to inherit the authentication carried out when a client first connected to an SMB server
 Inherited authentication in named pipes has become so ubiquitous and transparent that both Windows-users and programmers who use the Windows API often simply take it for granted

Implementation


Some services that operate over named pipes also allow MSRPC client programs to perform authentication

Over-rides the authorization provided by the SMB server

Only in the context of the MSRPC client program that successfully makes the additional authentication

Implementation


As another point of interest, SMB uses opportunistic locking


Special type of locking-mechanism
To improve performance

SMB serves as the basis for Microsoft's
Distributed File System implementation

Versions and implementations




Including the various protocols that extend SMB
For simplicity and conciseness and vagueness, however, the list omits mention of the extent or completeness of the reimplementation or porting status for any of these implementations
Lumps them all together simply as "SMB"

Versions and implementations

List…










Samba , a free re-implementation of the SMB protocol and of the Microsoft extensions to it, includes an SMB server and a command-line SMB client.
Samba TNG : a fork of Samba.
The Linux kernel includes two SMB client implementations that use the
Linux VFS , providing access to files on an SMB server through the standard file system API : smbfs and cifs.
ONStor Inc.
offers an SMB implementation that also supports NFS protocol so users can access the same data through both protocols.
Novell NetWare version 6 and newer has a CIFS server implementation providing access to NetWare volumes for Microsoft Network clients.
FreeBSD includes an SMB client implementation called smbfs that uses its
VFS .
NetBSD and Mac OS X include SMB client implementations called smbfs, originally derived from the FreeBSD smbfs; they use the NetBSD and OS X
VFS.
Solaris has a project called CIFS client for Solaris, based on the Mac OS X smbfs.
Sun Microsystems added in-kernel CIFS support to Solaris in October 2007
Sun Microsystems Cascade , which became known as PC-Netlink , represents a port of Advanced Server for Unix . Sun took over two years making the code useful, due to the poor quality of the original port.

Versions and implementations

Continued…












FreeNAS , a dedicated small-sized NAS server, runs FreeBSD for Network-attached storage (NAS) services, and supports protocols including CIFS/Samba
Advanced Server for Unix (AS/U) comprises a port of Windows NT 3.51's SMB server code to Unix . Microsoft licensed the code to AT&T , which then licensed it to major
Unix vendors. The poor quality of the original port (allegedly[ citation needed ] carried out by Microsoft itself) has caused any vendor sub-licensing it significant grief.[ citation needed ]
VERITAS Software has an implementation of SMB.
SCO has a port of Advanced Server for Unix .
SCO also has VisionFS , a Microsoft-independent re-implementation of SMB developed through reference to Samba source code.[ citation needed ]
Network Appliance has an SMB server implementation
Objective Development 's Sharity provides an SMB file-system client for Unix.
The Alfresco content-management system includes a Java implementation of SMB
JCIFS offers an implementation of SMB in Java
RTSMB , a CIFS/SMB implementation written in ANSI C. EBS designed RTSMB from scratch, independently of MS or SAMBA design reference, to run in embedded devices .
Visuality Systems NQ CIFS , a CIFS (SMB) server and client solution for embedded devices — ported to many popular real-time operating systems (RTOSs)
Thursby Software Systems offers a commercial implementation of SMB/CIFS for Mac
OS.