Introduction to Network Attached Storage (NAS)

Before you start

Objectives: Learn what is NAS, when it is used, and how it is configured.

Prerequisites: you should know what is SAN.

Key terms: NAS, description, network storage, server

 What is NAS

If we are implementing a file server on our computer network, and we need to implement huge amounts of storage space for our users to save their files, than we have two different options for adding storage to the network. The first option is to install our file server, and then install additional storage space in the server itself. This is called using direct attached storage. This type of storage actually exists inside the server machine, like in desktop systems. The second option is using the Network Attached Storage (NAS) device.

NAS device is a storage appliance that plugs directly to the network. NAS devices are usually rack mounted devices that have a file server. Usually they come with some kind of RAID array, measured in TB in storage space. NAS devices also have some kind of motherboard, together with the CPU and RAM. Also, NAS device will have a network interface. Many times it will have two or more network interfaces, which will allow us to combine interfaces to balance the load (adapter teaming). NAS devices will also have minimal Network Operating System (NOS) installed. On the network, NAS device is seen as a virtual file server. Client on the network won’t know the difference from the full file server and NAS device. The key difference between NAS and Storage Area Network (SAN) system is the fact that we use network protocols to access the storage on the NAS devices. When we are dealing with SAN, then the server that is connected to the SAN sees that storage as if it was directly connected to the server machine. NAS device connects to our network medium with its own cable, and we access it using TCP/IP network like Ethernet, while SAN uses Fiber Channel (encapsulated SCSI).

The two most popular network protocols to access NAS device are SMB (Server Message Block) and NFS (Network File System). SMB is the protocol used to access shared files on Windows systems (SMB on Windows is also known as CIFS – Common Internet File System), while NFS is used on Linux systems (NFS can be used on Windows as well). Almost any machine that can connect to the LAN can use NFS or CIFS to connect to NAS, while with SAN devices with SCSI Fiber Channel can connect to the SAN. With NAS clients can connect directly to the NAS unit to access data, while with SAN servers are connected to the SAN units and clients connect to servers (servers coordinate all data access).

NAS configuration

To configure NAS, most NAS devices come with built-in web server that runs on minimal NOS. We can access the web interface over network, from the client computer. The web interface will provide configuration options for NAS, like its IP address, etc. Usually, most NAS devices can be integrated with our existing server systems and server operating systems on our network. To be sure, we should always check the NAS device documentation before we buy it, just to be sure that is is compatible with our server OS.

NAS devices can be grouped together to a cluster to provide high degree of fault tolerance. We need to check NAS specification to see if it has support for clustering, although most of them will have clustering support. If we have one NAS on our network, and all our users save their data on it, we have a single point of failure. If something happens to that single NAS, all our users will lose access to their data. To get around this is to group NAS devices together to provide a degree of fault tolerance. To do that, we install multiple NAS devices on the network. Then we configure each NAS device to work together and function as a single unit. From the perspective of the clients on the network, this will appear to be a single NAS device. This provides a degree of redundancy, and we can configure them to load balance. That way we also get faster data transfer speeds. In addition, we have fault tolerance, because if one of the NAS devices go down, other ones in the cluster will start working instead of the one that went down. That way, our network will continue to run, while we repair or replace the NAS that went down. Users on the network won’t even notice that anything was wrong.