Network File Systems

NFSAFSSMB

NFS Generalhttp://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

DistributionDistinctive feature of a DFS:

System 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

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

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

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 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 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

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

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

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

Protocol development versus

Competing protocols

Protocol development versus competing protocols 1980s

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 data-encoding — 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 machine-architectures. 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

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 NFSv4.1 pNFS server:

A collection or community of server resources or components

Community members are controlled by the meta-data server

pNFS client still accesses a single meta-data server for traversal or interaction with the namespace Client moves data to and from the server

Directly interact with the set of data servers belonging to the pNFS server community

Present NFSv4.1 provides:

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 Part of the Andrew Project

Named for 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

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 read-only 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)

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 AFS includes Application ACLs (A)-(H)

which have no effect on access to files.

SMBhttp://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 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 inter-process 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 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 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.