Transcript Document

Network File Systems
NFS
AFS
SMB
NFS General
http://en.wikipedia.org/wiki/Network_file_system
Network File System
(NFS)

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
Distribution

Distributed File System (DFS)

Network file system with:
Clients, servers, and storage devices
 Spread throughout the machines of a distributed
system or intranet


Service activity occurs across the network

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

A DFS can be implemented:
As part of a distributed operating system
 By a software layer

 Managing the communication between conventional
operating systems and file systems
Distribution
 Distinctive
 System
feature of a DFS:
with many and
autonomous clients and servers
Transparency
Transparency

A DFS should appear to its users to be a
conventional, centralized file system

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
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

The performance of a DFS can be viewed
as one dimension of its transparency

Ideally, it would be comparable to that of a
conventional file system
Concurrent file updates
Concurrent file updates

A DFS should allow multiple client
processes on multiple machines to access
and update the same files


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
Network File Systems
Sample Network File Systems

Client-server file systems


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9P
Amazon S3
Coda
Secure File System (SFS)
Self-certifying File System (SFS)
Sample Network File Systems
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Distributed file systems
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Ceph
Andrew File System (AFS), OpenAFS
DCE Distributed File System
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
Google File System


Set of client and server services for organizing many distributed SMB file shares
into a distributed file system
GlusterFS


Distributed file system for large scale cluster computing
Microsoft Distributed File System


High performance distributed file system. It is also integrated with hadoop.
Lustre


Java software framework that supports distributed applications running on large
clusters of commodity computers
Kosmos FS


File system that is optimized for Google's core storage needs
Hadoop


Remote file access protocol used with the Distributed Computing Environment
Platform for developing clustering applications
Parallel Virtual File System

Parallel file system that focuses on high performance access to large data sets
NFS Protocol
http://en.wikipedia.org/wiki/Network_File_System_%28protocol%29
Network File System Protocol

Network file system protocol:

Allows a user on a client computer to access files over a
network
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


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
Versions and variations

Version 1


Sun used only for in-house experimental
purposes
Did not release it to the public
Versions and variations

Version 2 of the protocol


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

Version 3 (RFC 1813, June 1995) added:

Support for 64-bit file sizes and offsets


Support for asynchronous writes on the server

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Avoid the need to re-fetch them
READDIRPLUS operation


Improve write performance
Additional file attributes in many replies

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Handle files larger than 4 gigabytes (GB)
Get file handles and attributes along with file names
when scanning a directory
Assorted other improvements
Versions and variations

At the introduction of Version 3


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

Version 4 became the first version
developed with the IETF

After Sun Microsystems handed over the
development of the NFS protocols
Versions and variations

Version 4 includes:




Performance improvements
Mandates strong security
Introduces a stateful protocol
Defined by


RFC 3010, December 2000
Revised in RFC 3530, April 2003
Versions and variations

Various side-band protocols have become
associated with NFS, including:

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

WebNFS
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Allows NFS to




Integrate more easily into Web-browsers
Enable operation through firewalls
An extension to Version 2 and Version 3
Sun Microsystems open sourced their
WebNFS implementation

via https://yanfs.dev.java.net/
Platforms
Platforms

NFS most commonly used with UNIX
systems

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





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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
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





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
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

Exporting the names and parameters of directories
Typically using the /etc/exports configuration file and the exportfs
command
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
Protocol development
versus
Competing protocols
Protocol development versus
competing protocols

1980s



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NFS and ONC figured prominently in the network-computing war between Sun
Microsystems and Apollo Computer, and later the UNIX wars (ca 1987-1996)
between AT&T and Sun on one side, and Digital Equipment, HP, and IBM on the
other.
During the development of the ONC protocol (called SunRPC at the time), only
Apollo's Network Computing System (NCS) offered comparable functionality.
Two competing groups developed over fundamental differences in the two
remote procedure call systems. Arguments focused on the method for dataencoding — ONC's External Data Representation (XDR) always rendered integers
in big-endian order, even if both peers of the connection had little-endian
machine-architectures, whereas NCS's method attempted to avoid byte-swap
whenever two peers shared a common endianness in their machinearchitectures. An industry-group called the Network Computing Forum formed
(March 1987) in an (ultimately unsuccessful) attempt to reconcile the two
network-computing environments.
Later, Sun and AT&T announced that the two firms would jointly develop AT&T's
next version of UNIX: System V Release 4. This caused many of AT&T's other
licensees of UNIX System V to become concerned that this would put Sun in an
advantaged position, and it ultimately led to Digital Equipment, HP, IBM, and
others forming the Open Software Foundation (OSF) in 1988. Ironically, Sun and
AT&T had previously competed over Sun's NFS versus AT&T's Remote File
System (RFS), and the quick adoption of NFS over RFS by Digital Equipment, HP,
IBM, and many other computer vendors tipped the majority of users in favor of
NFS.
OSF solicited the proposals for various technologies, including the remote
procedure call (RPC) system and the remote file access protocol. In the end,
proposals for these two requirements, called respectively, the Distributed
Computing Environment (DCE), and the Distributed File System (DFS) won over
Sun's proposed ONC and NFS. DCE derived from a suite of technologies,
including NCS and Kerberos. DFS used DCE as the RPC and derived from AFS.
Protocol development versus
competing protocols

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
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Primary addition is Parallel NFS (pNFS)


Protocol defines a method of separating the meta-data (names
and attributes) of a filesystem from the location of the file data
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Holds the names of files and their data under the single umbrella
of the server
Products exist that are multi-node NFS servers


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

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A method of introducing data access parallelism
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

NFSv4.1 pNFS server:

A collection or community of server resources
or components


Community members are controlled by the metadata server
pNFS client still accesses a single metadata server for traversal or interaction
with the namespace

Client moves data to and from the server
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Directly interact with the set of data servers
belonging to the pNFS server community
Present
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NFSv4.1 provides:
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Sessions
Directory Delegation and Notifications
Multi-server Namespace
ACL/SACL/DACL
Retention Attributions
SECINFO_NO_NAME
AFS
http://en.wikipedia.org/wiki/Andrew_File
_System
Andrew File System
(AFS)

Distributed networked file system

Developed by Carnegie Mellon University


Named for



Part of the Andrew Project
Andrew Carnegie
Andrew Mellon
Primary used in distributed computing
Features
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
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

Cache consistency maintained by callback
When a file is cached
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
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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)


Only the changed portions copied back to the file server
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


Volumes are created by administrators



Links to other AFS volumes
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

The file name space on an Andrew
workstation is partitioned into a shared
and local name space

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

Andrew File System


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
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
Available permissions

The following Access Control List permissions can
be granted:

Lookup (l)


Insert (i)


allows a user to add new files or subdirectories to the
directory.
Delete (d)


allows a user to list the contents of the AFS directory,
examine the ACL associated with the directory and access
subdirectories.
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)


Write (w)


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.
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

AFS includes Application ACLs (A)-(H)
which have no effect on access to files.
SMB
http://en.wikipedia.org/wiki/Server_Message_Block
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"
Server Message Block
(SMB)

When discussing SMB, one should
distinguish:





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
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

Original design of SMB envisaged it
running on top of the NetBIOS and
NetBEUI APIs

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

Windows Vista introduced Server Message
Block 2.0
History

Side issue:

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
Implementation

Client-server approach

SMB works through a peer-to-peer approach


One section of the SMB protocol specifically deals with
access to filesystems, such that clients may make
requests to a file server


Client makes specific requests and the server responds
accordingly
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.

Windows Internet Naming Service (WINS) offers a suitable solution in Microsoft
environments.
Proper implementation of a NetBIOS Name Server (NBNS) can mitigate this
problem
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

In Microsoft Active Directory environments
Microsoft recommends the use of Dynamic DNS
Implementation

Performance issues

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's modifications

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

Points of interest

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

Points of interest

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

Points of interest

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
Versions and implementations

The following list explicitly refers to "SMB" as
including an SMB client or an SMB server



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
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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.