1. Introduction to Networks
Network Attached Storage

2. NAS Device
Alongside a file server or a SAN, our third option to provide shared network storage is a Network Attached Storage (NAS) device
A NAS device is a storage appliance that plugs directly to your network medium to provide file storage services
The NAS device is basically a pared-down file server that is designed and optimized to do one thing and one thing only: store files for network users
Because it's optimized to provide network storage, a NAS device can typically provide better performance than a standard file server
This is because a file server needs to fulfil numerous network roles in addition to file storage, such as being a domain controller, a web server, or even a hypervisor for virtual machines. Also, the operating system in the file server won’t be designed solely for file storage

3. NAS Device Hardware A NAS device typically consists of:
A RAID array with terabytes of storage space.
A basic motherboard with a processor and memory.
One or more network interface cards
A minimal network operating system
Note that low-end (home use) NAS devices may have only one interface. High-end NAS devices will usually have multiple network interface cards to allow you to configure adapter teaming
With teaming, you 'bond' multiple network adapters together and assign them a single IP address to double your network throughput, similar to Etherchannels. Because a NAS device must handle many network I/O operations from many network users simultaneously, teaming can be a very advantageous feature to implement.

4. NAS Installation
After installing and configuring a NAS device on your network, it will appear to other network hosts to be a typical file server with shared folders that can be accessed over the network medium
Client systems will access the NAS device to read and write files in the same way that they access shared storage on a standard file server
This is because NAS devices use standard network protocols to provide read and write access to files on the device, including -
Server Message Block (SMB) (also known as the Common Internet File System (CIFS))
Network File System (NFS)

5. NAS Configuration
To configure the device, most NAS appliances provide a web-based interface that you can access using a browser on your workstation
The web-based interface provides access to all of the configuration settings used by the device, such as its IP address, subnet mask, security settings, etc.
You can usually integrate the appliance with your existing network environment. For example, you can usually join a NAS device to your Active Directory domain
This allows you to use your existing domain user accounts to authenticate to the device and to manage access to the data stored on it. Otherwise, you would have to configure duplicate user accounts on the device itself to allow your network users to authenticate to it

6. Single Point of Failure
One of the key problems with implementing a NAS device is the fact that it creates a single point of failure for the file services on your network
If all of your network users save their files on the NAS device and it fails for some reason, the data becomes unavailable until you replace the device and restore the data from backup
On a large network, this could take days to accomplish
Just like with a storage area network, we can prevent this with clustering

7. Clustering for Data Protection
With clustering enabled, multiple NAS devices can be grouped together in a cluster to provide a degree of fault tolerance
All of the data is replicated between the devices, and to users on the network, the cluster appears as a single file server
If one of the devices in the cluster goes down, the other devices immediately take over and continue providing access to the files
This is called a failover, and it usually only takes a second or two to complete
This is much more tolerable than the several days of downtime associated with the failure of a single NAS device

8. Clustering For Load Balancing
Clustered NAS devices can also be configured to load balance
If the storage provided by the cluster is heavily accessed by network users, it could potentially create a bottleneck and degrade performance
Using a load-balancing cluster, the network traffic destined for the shared storage can be divided up and distributed between multiple devices in the cluster
This can dramatically speed up performance of the storage system
This should sound very familiar to clustering on a storage area network, since it works the same way

9. SAN vs NAS
Generally speaking, a fibre channel SAN will provide better performance than a NAS deployment. This happens for two reasons -
An FC SAN has its own dedicated storage area network that is independent of the production network. A NAS, on the other hand, is connected directly to the production network and must compete for bandwidth with other network hosts
An FC SAN uses the block-level SCSI protocol to manage storage I/O operations. A NAS device, on the other hand, uses file transfer network protocols (such as SMB) to manage storage I/O. File transfer operations are slower than block-level operations.
SANs do have one drawback, however. SANs are much more expensive to implement than a NAS deployment
Also note that an iSCSI SAN can either have its own network, or be on the production network