By Pierre-Jean Alzieu / Alexandre Botella
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Network Attached Storage systems—more commonly known as NAS—are file servers allowing you to access files from across your network, or even over the Internet from a remote location.

Currently best-known in the business world, NAS storage systems are beginning to interest more and more home users.  They're a great solution if you have files to share across several different computers.  Because they usually include more than one hard drive, they allow you to safeguard your data by creating a RAID array.  As we'll see, though, they're not just useful for storing files, and some models can also run FTP, e-mail or printing servers on your home network.

A word about RAID

RAID is an acronym that stands of a Redundant Array of Independent Disks, and it allows you to save files across several hard drives at once.  The extent to which the system is fault-resistant depends on how you configure it:

RAID 0 significantly improves performance by working over several hard drives in parallel.  If you have two drives, for instance, half of the data is written to one half to the other.  If either one of the drives fails, you lose all of the data.  This is a configuration to avoid.

RAID 1 is often used in NAS systems to improve data security.  It essentially creates a mirror of the first hard drive on the second, with the NAS constantly keeping the two drives in sync.  If one or the other of the two drives fails, then all of its data is entirely recoverable from the other.  Unfortunately, though, such reliability comes at a price: if you want to be able to store 1 TB of data, then you'll need two 1 TB drives.

If you want to use all of the storage capacity that you have, you can also use Jbod mode, which simply strings the hard drives out one after the other to create a single file system.  The performance is not as good as with RAID 0, and your data is less secure than it would be with RAID 1.

The main uses and protocols

As you'll see in our tests of individual products, the options available vary from one manufacturer to another.  However, there are a few standard features, including support from the CIFS/SMB protocol to access your NAS over a Windows network, the ability to run an FTP server and individual user accounts.

Protocols: as well as CIFS/SMB, some NAS systems support the AFP and NFS protocols so you can use them with Mac and Linux networks.  It's also possible to access your data from offsite, with some products offering the choice between FTP and HTTP, with encrypted connections for extra security.

Backup: by their very nature, NAS systems have an important role in backup.  Some allow you to copy the entire system to an external peripheral, and the opposite is of course also possible.  Some manufacturers include a dedicated hotkey to immediately backup an external hard drive or USB flash drive.

Downloading: although NAS systems are in theory designed for storage, they can also do other things.  Almost all of the models we've tested include some ways of downloading content, with some manufacturers sticking resolutely to FTP/HTTP while others support BitTorrent with advanced download management.

Web Server:
this feature allows you to manage your files over an Internet connection.  Just use a web browser to log into your NAS server and you'll be able to download, copy, move, delete and rename all of the files that you've saved there.

as you might have noticed, NAS systems offer a lot of features.  Some also allow you to publish music, videos and photos online.  Others work as multimedia servers, which means DLNA-compatible equipment can access the files they contain directly over the network.  However, because of the various problems associated with compatibility between different file formats, we recommend you use an NAS system as a simple file server.  If you really want a multimedia system, then connecting a dedicated media centre to your network will avoid such problems and provide better performance than NAS.

Note: if you want to match the performances that we measured in our tests, all of the different components in your network need to support Gigabit Ethernet—the Wi-Fi routers provided by ADSL ISPs usually don't.
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