What is the Storage Area Network (SAN)?

SAN is a technology where storage has been moved into the network rather than directly connected to the servers. In this tutorial, we will learn what is Storage Area Network(SAN), Unit of storage (LUN), Protocols and its advantages, and disadvantages.

What is SAN?

SAN stands for Storage Area Network. It is a high-speed, dedicated network that has interconnected storage devices. The network consists of Fibre switches and cables. Servers use SAN as a shared pool for storing files and data.

What is Local Storage?

In traditional storage, each server has its own dedicated hard drives that are local to the server. All files and application data are saved in those drives. With time increase in the number of applications and data, the drives start getting exhausted. For example, if a company runs a web server with shared hosting, there will soon be no space for additional websites.

While other servers may have free space, but the overloaded server can not access it. The solution is to add more storage on the loaded server. But it is time-consuming and adds some additional cost.  Again note that the free space is there with other servers, but you can not use it. This brings a need for a pool that has multiple hard drives, and a server can use a portion or full.

Storage when NO SAN is used.

How does storage work with SAN?

With the SAN, the storage becomes shared and works as a pool of storage segments.  A  server may initially opt for basic storage and later can scale up dynamically without adding any new hardware.

Storage with SAN using switch
Storage with SAN using fiber switch

What is LUN?

LUN stands for logical unit number. All devices execute input/output assigned a logical unit number.  A computer uses LUN to work with the storage device as defined by the Small Computer System Interface (SCSI). SCSI works for data transport between services and storage devices using transport protocols such as Internet SCSI and Fiber Channels. The server has a SCSI client, and storage has a server or LUN.

The LUN identifies a full storage device, a collection of storage devices, or a part of a large storage device on the host computer. An admin can assign the permissions of specific LUNs.

What are the advantages of using SAN?

  • Centralize Access: The storage is central. It brings easy-to-implement new policies.
  • High-Speed Network: The switch and cables are based on fiber optics. This brings tremendous speed while accessing data. A computing device has the impression that data is locally present.
  • Fast recovery after failure: The processing servers and all storage (applications and data) are decoupled. So when server hardware fails, all data is still present to recover business. Once the server returns to business, it loads data and starts working immediately.
  • Failover – When a server fails, another server in SAN start processing the data requests. It does automatic rerouting to the backup storage.
  • Scaling –  Any time more storage devices can be added to the SAN if applications require more capacity.
  • Security –  There can be user-based access for the storage so that only an allowed person can access it.

Are there any disadvantages of SAN?

There are a few disadvantages to SAN. The first is the initial cost. A storage area network requires a high initial setup cost as compared to traditional storage.

Cloud storage and SAN?

An increasing number of businesses are using the cloud for servers and storage. A cloud service can be only for data storage too. There are many companies that are providing services. With the cloud, one can choose minimal storage to start with and keep increasing as required. 

The difference between SAN and the cloud is that SAN is local to a company with servers connected to storage with high-speed switches and fibers. While storage in the cloud is through the internet, that may bring latency. A company may choose a hybrid approach, where lesser-time critical storage is in the cloud and critical in the local SAN.

Communication Protocols for SAN:

The server and storage connect to each other over a network. When a  server needs to access the storage, it issues a command to the storage and, in answer, gets the requested files or other resources. Like other network communication, there are protocols between the two communicating platforms. Following is a list of protocols for the storage area network.

  1. Fibre Channel Protocol (FCP)
  2. Fibre Channel Over Internet
  3. NVME
  4. iSCSI