Describe the Network File System and Network File Services

When stand-alone computers ruled the computer industry, users shared files with 8-inch floppy disks or cassette tapes.
When the hardware and protocol for networking computers became available, users needed a convenient way to transfer files and share resources among computers. The first mechanism to transfer files was FTP^[1], but using it was cumbersome: users paused their session, moved some files with the FTP client, and then resumed their session.

A Network File System (NFS) and a non-network File System differ primarily in how they are accessed and managed:

1. Network File System (NFS):
   • Access Over Network: NFS allows files to be accessed over a network, enabling users to work with files as if they were on a local drive, even though they are stored on a remote server.
   • File Sharing: It facilitates file sharing among multiple users and systems across a network. Users on different machines can access and share the same files concurrently.
   • Centralized Storage: Files are stored on a centralized server, making it easier to manage backups, security, and access controls.
   • Protocol-Based: NFS uses specific network protocols (like NFS protocol, SMB/CIFS) to manage file access over a network.
2. Non-Network File System (Local File System):
   • Local Access: Non-network file systems are typically used for accessing files stored on local storage devices, such as hard drives, SSDs, or external USB drives.
   • No Network Dependency: Files are accessed directly from the storage device attached to the local computer, with no need for a network connection.
   • Limited to One User/System: Usually, only the user of the system on which the storage device is attached can access the files. There's no built-in mechanism for sharing files over a network.
   • Examples: Common examples include ext4, NTFS, HFS+, FAT32, which are used by Linux, Windows, and macOS systems respectively.

Summary:

• NFS is designed for accessing and sharing files over a network, making it suitable for environments where multiple users or systems need to access the same data from different locations.
• Non-network file systems are designed for local access on a single machine, without the need for network capabilities or multi-user access.

Preventing congestion in networks is essential for maintaining efficient data flow and ensuring that network performance remains high. Here are several measures that can be taken to prevent or alleviate network congestion:

1. Traffic Shaping and Policing:
   • Traffic Shaping: This involves controlling the flow of data entering the network to ensure that it adheres to a predefined rate, smoothing out bursts of data and reducing the chances of congestion.
   • Traffic Policing: This technique monitors the data rate and can drop packets or mark them for lower priority if they exceed certain thresholds, helping to prevent congestion.
2. Quality of Service (QoS):
   • Prioritization: QoS mechanisms can prioritize certain types of traffic (e.g., VoIP, video streaming) over others, ensuring that critical services have enough bandwidth and are less likely to be affected by congestion.
   • Bandwidth Reservation: Reserving bandwidth for high-priority traffic can help prevent congestion by ensuring that sufficient resources are available for essential services.
3. Load Balancing:
   • Distributing Traffic: Load balancing techniques distribute network traffic across multiple servers or network paths, preventing any single resource from becoming a bottleneck.
   • Redundancy: Implementing multiple paths and failover mechanisms ensures that traffic can be rerouted in case of congestion on a particular path.
4. Congestion Control Algorithms:
   • TCP Congestion Control: Protocols like TCP have built-in congestion control algorithms (e.g., TCP Reno, TCP Cubic) that dynamically adjust the rate at which data is sent based on the level of network congestion.
   • Explicit Congestion Notification (ECN): ECN allows routers to mark packets instead of dropping them when congestion is detected, signaling the sender to reduce its transmission rate.
5. Network Capacity Planning:
   • Capacity Upgrades: Regularly upgrading network infrastructure to increase bandwidth and capacity can help prevent congestion as traffic demands grow.
   • Scalability: Designing networks with scalability in mind ensures that additional capacity can be added easily as the network expands.
6. Efficient Routing Protocols:
   • Dynamic Routing: Using dynamic routing protocols (e.g., OSPF, BGP) that can adapt to changing network conditions helps avoid congested routes.
   • Shortest Path First (SPF) Algorithms: SPF algorithms calculate the most efficient routes, helping to minimize congestion by avoiding overuse of certain network paths.
7. Packet Scheduling:
   • Fair Queuing: This ensures that no single flow can monopolize the network resources by fairly distributing bandwidth among different traffic flows.
   • Weighted Fair Queuing (WFQ): WFQ extends fair queuing by allowing different weights to different types of traffic, giving more bandwidth to higher-priority traffic.
8. Network Segmentation:
   • VLANs and Subnets: Segmenting a network into smaller, manageable pieces can reduce congestion by limiting the broadcast domain and isolating traffic within specific segments.
   • Virtual Private Networks (VPNs): VPNs can help reduce congestion by optimizing the routing of traffic between distant locations.
9. Caching and Content Delivery Networks (CDNs):
   • Local Caching: Storing frequently accessed content closer to the users reduces the load on the core network and helps prevent congestion.
   • CDNs: CDNs distribute content across multiple geographically dispersed servers, reducing the strain on any single network path or server.
10. Network Monitoring and Analysis:
    • Real-Time Monitoring: Continuously monitoring network traffic can help detect early signs of congestion and allow for proactive measures.
    • Traffic Analysis Tools: Using tools to analyze traffic patterns and identify congestion points can guide decisions on where to add capacity or apply traffic management techniques.

By implementing these measures, network administrators can significantly reduce the risk of congestion and maintain efficient, high-performance networks.

Enter the Network File System or NFS. NFS allows users to manipulate files on a remote computer as if they were local. NFS transparently supports the usual file operations, including:

1. copy (cp)
2. move (mv)
3. delete (rm)
4. link (ln)
5. list (ls)

NFS frees users from the inconveniences of FTP. A user can access and modify files anywhere on the network using the standard command-line programs.

NFS operates using the common client-server model. NFS servers can export entire filesystems, optionally making them publicly available and NFS clients then mount the exported filesystems.
Once mounted, the server's remote filesystem is attached to the client's local filesystem.
When any file modifications on the NFS filesystem occur, the NFS client sends the modifications to the NFS server for processing.
Client-server model: A computer design model, where servers offer up one or more services for client use.
The next lesson discusses the relationship between NFS and remote procedure calls.

[1] File Transfer Protocol (FTP): FTP is one way to move a file from computer to computer.