Explore the differences between these two approaches to storage and file sharing.

What is SAN?

A SAN (storage area network) is a tightly coupled, dedicated network of storage devices that provides a shared pool of storage and appears to each user on the network as if it were connected directly to the computer. A SAN connects via Fibre Channel and uses switches to manage storage data traffic. It is designed for quick, low-latency data access and easy scalability.

What is NAS?

NAS (network-attached storage) refers to a file-level storage server connected to a computer network, providing data access to a group of users on that network. A NAS system connects via an Ethernet network and has redundant data structures for resiliency. It’s designed to be an affordable and easy-to-maintain network storage option.

How SAN works

SAN storage solutions are block storage-based, meaning data is split into storage volumes that can be formatted with different protocols, such as iSCSI or Fibre Channel Protocol (FCP). A SAN can include hard disks or virtual storage nodes and cloud resources, known as virtual SANs or vSANs.

SAN configurations are made up of three distinct layers:

  • Storage layer: The physical data storage resources, such as drives in a data center, are organized into storage pools and tiers. Because the data is stored using block-level storage, built-in redundancy and automatic traffic rerouting, data is available even if a server is down.
  • Fabric layer: The fabric layer is how the storage connects to the user, such as via network devices and cables. This connectivity could be via Fibre Channel or Fibre Channel over Ethernet (FCoE). Both take pressure off the local area network (LAN) by moving storage and associated data traffic to its own high-speed network.
  • Host layer: The servers and applications that facilitate accessing the storage. Because this layer recognizes the SAN storage as a local hard drive, it ensures quick processing speeds and data transfers.

When User A wants to collaborate on a file with User B, who is at another location, they will look up the file on a networked device, triggering a request to access a file made at the host layer. The request is then processed through a server across the network, or fabric layer, using data access protocols. The data is then retrieved from the data pool within the storage layer. User A can make changes, and because SANs deliver low-latency data storage and updates, User B can access the file, see the changes and add their own changes in real time.

Another approach to SAN storage is through a vSAN (i.e., a virtual storage area network). Instead of storing data on hardware like a data drive, vSANs provide storage on virtual machines (VMs), often hosted on a server. VMs are the fundamental units in cloud computing, allowing companies the ability to run and scale applications and workloads effectively and efficiently. A vSAN taps into the flexibility, scalability and security of cloud computing for shared storage and data access throughout an organization and at various locations.

How NAS works

NAS storage systems are file storage-based, meaning the data is stored in files that are organized in folders under a hierarchy of directories and subdirectories. Unlike direct attached storage — which can be accessed by one device — the NAS file system provides file storage and sharing capabilities between devices.

A NAS system is built using the following elements:

  • Network: One or multiple networked NAS devices are connected to a local area network (LAN) or an Ethernet network with an assigned IP address.
  • NAS box: This hardware device with its own IP address includes a network interface card (NIC), a power supply, processor, memory and drive bay for two to five disk drives. A NAS box, or head, connects and processes requests between the user’s computer and the NAS storage.
  • Storage: The disk drives within the NAS box that store the data. Often storage uses a RAID configuration, distributing and copying data across multiple drives. This provides data redundancy as a fail-safe, and it improves performance and storage capacity.
  • Operating system: Unlike local storage, NAS storage is self-contained. It also includes an operating system to run data management software and authorize file-level access to authorized users.
  • Software: Preconfigured software within the NAS box manages the NAS device and handles data storage and file-sharing requests.

When a user makes a request for a file stored on a NAS, the request is sent to the NAS box, the request is managed by the operating system and software, while the data is retrieved using protocols, such as SMB (server message block) — an application-level protocol used for shared access to files — or NFS (network file system) — which allows users to view, store and update files in a remote system. The data is then sent in packets to the user’s device using the TCP/IP protocol via a central server, or switch.


Both SAN and NAS systems are network-based storage solutions aimed at providing multiple users 24/7 access to data on-premises and remotely. Here are some differences between the two approaches.

  • Type of network: NAS is connected to devices using a LAN or Ethernet network, while a SAN runs on high-speed Fibre channel.
  • Ease of management: NAS storage options are typically easy to set up and manage, with options available for both small businesses and enterprises. SAN requires more hands-on administration to configure and manage.
  • Protocols: Protocols give devices a way to communicate with one another and provide a standardized set of rules for formatting and processing data. NAS can use several protocols to connect with servers, including NFS, SMB/CIFS, and HTTP; a SAN uses the SCSI protocol.
  • Scalability: Both SAN and NAS solutions can scale up storage by adding additional storage. Simple NAS configurations can easily be scaled by simply adding more NAS boxes; however, on the enterprise level, this can add complexity and become expensive. SANs are highly scalable because more block-level storage devices can be added over time without affecting network integrity.
  • Speed and performance: With their shared pool of storage, SANs are low-latency solutions, while NAS systems often have slower throughput when retrieving shared files.
  • Price: Entry-level NAS solutions are an affordable option for individual users. Companies can also affordably meet certain storage needs with NAS. Because they require more management and have a more complex storage architecture, SANs are often the more expensive option.

NAS use cases

There are times when NAS is the better choice, depending on the company’s needs and application:

  • File collaboration and storage: This is the primary use case for NAS in mid- to large-scale enterprises. With NAS storage in place, IT can consolidate multiple file servers for ease of management and to save space.
  • Archiving: NAS is a good choice for storing a large number of files, especially if you want to create a searchable and accessible active archive.
  • Big data: NAS is a common choice for storing and processing large unstructured files, running analytics and using ETL (extract, transform, load) tools for integration.

SAN use cases

Low-latency and scalability make SANs the preferred choice in these cases:

  • Video editing: Large files require high throughput and low-latency. SANs can connect directly to the video editing desktop client, without the need for an extra server layer, offering high-performance capabilities.
  • Ecommerce: Today’s consumers expect shopping online to go smoothly and quickly. Ecommerce companies need high-performance functionality, which makes SANs a good choice.
  • Backup/disaster recovery: Backups of networked devices can be executed quickly and directly to SAN storage because traffic does not travel over the LAN. Virtualization accelerates the processing and scalability of SANs with virtual machines and cloud storage.


Companies today have a wide range of storage technologies to choose from. That’s why it’s important to understand the different options, their functionality and the right use cases for the different storage methods. IBM offers a number of storage solutions to address today’s modern business needs.

To learn more about the power of SAN, read our overview of storage area networks and IBM’s SAN solutions.

Network-attached storage plays an important role in maintain business data reliably. IBM’s NAS solutions, offered through Tivoli Storage Manager, help businesses protect themselves against data failures.

Want to learn more about your data storage options? Read our overview — “What Is Data Storage?” — to compare options and learn about the solutions IBM offers.


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