Dfs Meaning – What Is DFS (Distributed File System)
What is the meaning of DFS
DFS Meaning – Dfs stands for Distributed File System.
Dfs is a system that allows a program to store and access remote files exactly as they do locally stored files.
Dfs Programs allow users to access files from remote computers present in the network.
What is DFS Meaning
In DFS, multiple clients or users share files offered by the shared file system. In the DFS communication between programs or processes is done using these shared files present in the network.
In DFS clients or users access files and folders that are provided by the file servers.
The client gives the request and the server provides a service to the client through a file service interface.
Service fulfills the request of the client by providing the requested file view, part of the file view, or folders.
The file view provided by the server to different clients may be different in accordance with the needs and prescribed authorizations.
Clients can only see those file views for which the client is authorized to access. Clients can do the following operations according to authorizations
- Creating files
- Reading files
- Writing files
- Deleting files
- Updating files
Depending on the predefined implementation all these operations may be performed on the files present on the server or on the local copies of the files.
The important challenges of distributed systems apply to DFS are as below:
Transparency of Dfs
Dfs must be completely transparent to ensure the following to its users
- Location
A Dfs user or client cannot informed be about the exact location of file the client is accessing
- Migration
In DFS a file can be transparently moved from one server to another
- Replication:
In D multiple copies of the same file may present
- Concurrency:
At the same time, multiple clients can access the same file in DFS.
Flexibility of DFS
In a flexible DFS, it must be possible to add or replace file servers. Also, a DFS
should support multiple underlying file system types (e.g., various Unix file systems, various
Windows file systems, etc.)
Reliability of DFS
In DFS reliability must be ensured to provide the following features.
- Consistency:
Due to replicated copies of a file and permitted concurrent access to files inconsistency may occur in the data
- Security:
In DFS each and every client must authenticate themselves before using a file and servers must decide whether the clients are authorized to do the requested operation. Also, communication between clients and the file server must be done with complete security.
- Fault tolerance:
In DFS all the clients should be able to work continuously if a file server crashes. Similarly, data must not be lost. Also, a restarted file server must be recovered to a valid state.
Performance of DFS
To provide a good performance it is essential that the DFS distribute requests across the multiple servers.
Moreover, multiple servers may be needed if the data file is very large.
Scalability of DFS
A scalable DFS must avoid the following
- Centralized components such as a centralized naming service,
- Centralized locking facility, and
- Centralized file storage
A scalable DFS must be capable to manage an increasing number of clients and files.
Scalable DFS must also be able to manage the growth of data files and clients over a geographic region and different administrative domains.
What is a distributed file system with example
Examples of Dfs
- Network File System (NFS)
- Andrew File System (AFS)
- Coda
- Google File System
- Ficus
- Rover
Coda
Coda is a distributed file system. It is developed as a research project at Carnegie Mellon University since 1987 under the direction of Mahadev Satyanarayanan.
It descended directly from an older version of the Andrew File System and offers so many similar features.
The predecessor of many distributed file systems that can be used for mobile operation is the Andrew file system (AFS, (Howard, 1988)).
Coda is the successor of AFS and offers two different types of replication:
- Server replication and
- Caching on clients.
Disconnected clients work only on the cache, i.e., applications use only cached replicated files.
Coda is a transparent extension of the client’s cache manager.
This very general architecture is valid for most of today’s mobile systems that utilize a cache.
It has many features that are desirable for network file systems. Currently, Coda has several features that are not found elsewhere.
- Dfs allows disconnected operation for mobile computing
- It is freely available under a liberal license
- Dfs gives high performance through client-side persistent caching
- It supports server replication
- Coda provides a security model for authentication, encryption and access control
- It continued operation during partial network failures in the server network
- It supports network bandwidth adaptation
- It has a good scalability
- Coda has well-defined semantics of sharing, even in the presence of network failures
Ficus
Important features of Ficus distributed file system are as follows-
- Ficus is a distributed file system, which is not based on a client/server approach.
- Ficus allows the optimistic use of replicates, detects write conflicts, and solves conflicts on directories.
- Ficus uses so-called gossip protocols, an idea many other systems took over later.
- A mobile computer does not necessarily need to have a direct connection to a server.
- With the help of other mobile computers, it can propagate updates through the network until it reaches a fixed network and the server.
- Thus, changes in files propagate through the network step-by-step.
- Ficus tries to minimize the exchange of files that are valid only for a short time, e.g. temporary files.
- A critical issue for gossip protocols is how fast they propagate to the client that needs this information and how much unnecessary traffic it causes to propagate information to clients that are not interested.
Mio-NFS
The system mobile integration of NFS (Mio–NFS) is an extension of the Network File System (NFS, (Guedes, 1995)).
In contrast to many other systems, Mio-NFS uses a pessimistic approach with tokens controlling access to files.
Only the token-holder for a specific file may change this file, so Mio-NFS avoids write conflicts.
Mio-NFS supports three different modes:
- Connected: The server handles all access to files as usual.
- Loosely connected: Clients use local replicates, exchange tokens over the network, and update files via the network.
- Disconnected: The client uses only local replicates. Writing is only allowed if the client is token-holder.
Rover
Compared to Coda, the Rover platform uses another approach to support mobility (Joseph, 1997a, and 1997b).
Instead of adapting existing applications for mobile devices, Rover provides a platform for developing new, mobility aware applications.
Two new components have been introduced in Rover.
- Relocatable dynamic objects are objects that can be dynamically loaded into a client computer from a server (or vice-versa) to reduce client-server communication.
A trade-off between transferring objects and transferring only data for objects has to be found.
If a client needs an object quite often, it makes sense to migrate the object.
Object migration for single access, on the other hand, creates too much overhead.
- Queued remote procedure calls allow for non-blocking RPCs even when a host is disconnected.
Requests and responses are exchanged as soon as a connection is available again. Conflict resolution is done in the server and is application-specific.
What are the advantages of DFS
The advantages of DFS are huge.
- It provides better organizations of file sharing between the groups and members of organizations
- It increased flexibility for storage data resources and better administration of data
- It gives an efficient solution to several business problems, like load-balancing and access to file shares
- It also provides better ways of disaster recovery methods for file shares.
What are the characteristics of a distributed file system
Important characteristics of DFS are as follows-
Transparency
Transparency includes all kinds of transparency such as location transparency, network transparency, replication transparency, migration transparency, concurrent transparency, and failure transparency
User Mobility
Users should be able to access the required file during the mobile environment. It includes both kinds of mobility device mobility and user mobility.
Performance measurement
It means the DFS must be robust and can be accessed during the failure of the system also.
Heterogeneity
File services must be accessible via different operating systems and different hardware.
Scalability
The DFS must be scalable at any length according to the need.
What are the requirements of DFS
The main requirements of DFS are Transparency, fault tolerance, and availability in all the circumstances to its users.
What is the purpose of DFS
A DFS manages all the files and folders across multiple computers. It similar to the traditional file system but DFS is managed to provide file storage and access over all kinds of networks like LAN, MAN, and WAN.
Dfs Meaning is a system that allows its users to access and share data files remotely, and transparently through multiple computers connected via the internet.