Network Attached Storage for home and office

NAS systems have come a long way the last few years, and have become much more accessible and popular for the computer user – home afficionado and SMB owner alike – in price, configuration and availability. But what is a NAS exactly, and why would you need one?

Introduction

NAS stands for Network Attached Storage, basically any storage that connects to your computer(s) through a network cable instead of a SATA, SCSI, FireWire or USB cable (those are called DAS – Direct Attached Storage). The main advantages are that everyone on the network can access the same data, and use it as a common hard drive for file sharing, backup and anything you can think about.

Gone are the days that every computer at home or in the office needed its own external hard drive for daily backups and added to the existing cable spaghetti, no more tapes or drives to store away or to put on a colleague’s desk. There are however – you guessed it – quite some variations on this theme. We will discuss the three main categories in more detail, each with their own particular set of benefits and disadvantages.

The external drive with Ethernet

The most simple of these NAS systems consists of what looks like a regular external hard drive, with an Ethernet port as an extra connection, and some extra hardware inside. Connecting it to the network is a straightforward operation: usually there is little or nothing to configure. The network address is gotten from the DHCP function of your network router, a standard share is set up, with a standard name, and access to all files to all users on the network. Some exceptions exist, but only on the pricier models. This is excellent for a small home network where everybody trusts one another and disk failure is not a catastrophe.

But that’s also it’s downside: anything else than an out-of-the-box configuration – other IP-ranges, security, separate shares and access rights – are usually missing. And these little boxes tend to overheat and let the standard hard disk die rather fast, unless they’re equipped with a decent – but noisy – fan. The cheapest ones have only 100 Mbit/s Ethernet (realistically 2 Megabytes/sec), and only the more expensive models have Gigabit Ethernet (ten times as fast).

The RAID box

Lately, more interesting NAS systems have been hitting the home and SOHO market, generally described as RAID boxes. These are basically small computers, with their own custom operating system (a.k.a. firmware) usually based on a small but reliable Linux kernel, two or more drives to guard against data corruption or to enhance speed in the corresponding RAID configuration, or simply linking all the drives together as one big volume in what is known as JBOD – Just a Bunch Of Disks.

The benefits are multiple: RAID levels protect against data loss through a failing hard disk, disks can be concatenated or striped for maximum size or speed, and separate shares created each with their designated users, quotas and access rights. Moreover, almost anything you would normally use a dedicated networked computer or small server for, can be done with these NAS boxes: backups, encryption, night time downloading, small scale web server and FTP server, … you name it.

What is also gaining in popularity, is their ability to blend in with our digital lifestyle: applications for uPNP file sharing, Audio/Video media straming (movies and music) to various appliances such as digital music players, TV, sound system, your X-Box, PlayStation, Wii, Home Theater PC, are just the tip of the iceberg.

Connectivity is usually Gigabit Ethernet, with the possibility to use Jumbo frames in order to reduce the TCP/IP overhead on the network. Unfortunately, the average PC hardware and its Windows operating systems can rarely benefit fully from this possible turbo speed. In practice, speeds are usually limited to 20 Megabytes/second, which isn’t bad at all. Furthermore, some devices have an extra USB port for easy configurability, which can also be hacked through software to attach a printer or external hard disk.

You can usually choose between two versions of each model: populated (with hard disks) or empty. The latter option allows you to start out with one (small) drive, and insert more or larger drives when you need them. Check the documentation and firmware for the possibilities, as not every NAS firmware is created equal. Some will require you to first move your data to one of the computers on the network in order to reformat the RAID array with the new disk(s), others will expand and rebuild the array in the background without you even having to reboot the system.

The embedded firmware – actually a small Linux kernel – can easily be upgraded to incorporate new functionality, but it gets even better. Some devices – such as the D-Link DNS-323 and successors – support a so called “funplug”, which makes the NAS boot a more extensive Linux operating system from one of its hard disks. From there on, an array of customizations and extensions are possible with additional applications that run 24/7. Regulating the fan speed with the temperature, synchronizing the internal clock with an official internet time source, P2P file sharing, elaborate backup schemes, network recycle bin (something Windows cannot do), connecting with different clients on different platforms (Windows, Mac, Linux), file journaling to revert human error, etc.: the possibilities are endless.

The corporate NAS

The corporate NAS is an entirely different beast. Things like iSCSI, Jumbo Frames for TCP/IP, a variety of network protocols to talk with all sorts of software platforms and legacy systems, the presence of redundant power supplies, and rack-mountability are just a few things that make these systems very reliable, compatible, fault tolerant, and pricey.

Capacities of these corporate NAS systems – sometimes called data filers – range between a few and several hundreds of Terabytes. The beauty of these systems – more precisely, their industrial-grade firmware – is that you can add and/or mix and match the number and size of installed hard drives as you go. The system then automatically rebuilds the RAID array in the background, without having to reboot or interrupt your workflow.

The redundant power supplies are no luxury: when these drives are mounted in a rack in the company’s server room, the stacked systems can get quite hot even when there is adequate air conditioning and cooling available. After all, the power supply is yet another component that cannot be part of a single-point-of-failure scenario in an enterprise environment.

And of course, you don’t populate these boxes with off-the-mill cheap desktop hard drives. For maximum performance and reliability, you’ll want to either buy an enclosure with manufacturer-specified drives already inserted, or go with specialized RAID drives.

Specially designated RAID hard drives withstand vibrations better, support staggered spin-up (so there is no power peak on start-up), and are designed to run 24/7 in adverse conditions for a very long time. When your business depends on data availability, you’ll probably have other things to do than keep a closet of spares on hand, or spend your time swapping hard drives.

Needless to say that in these environments where industrial standards and redundancy are key, it’s not just SATA that is used as the hard drive interface of choice. SAS (Serial Attached SCSI) has a larger market share, building on the popularity of SCSI in enterprise environments over the past few decades.

For ultimate redundancy, some manufacturers opt for dual-ported fibre-channel drives, where each drive is attached to two separate NAS filer heads, eliminating another single-point-of-failure. This avoids building a mirror of a mirror, where all data would have to be replicated on four different sets of hard disks in order to ensure fault tolerance.

iSCSI – basically SCSI hard disk connectivity over network cable – is used extensively as a replacement for the standard TCP/IP network protocol, as well as TCP/IP with Jumbo frames to get the maximum out of the data pipe. The connectivity options can also vary: Gigabit Ethernet over copper (UTP cable), 10 Gigabit Ethernet over fibre, or even 40 Gigabit Ethernet over InfiniBand. Upgrading connectivity and speed is as simple as swapping out the corresponding network module.

There is a great variety in this class of NAS boxes, with each manufacturer toting his unique benefit as the must-have feature. Depending on your intended application, your mileage (and budget) may vary. If you have the choice, you may want to go for the device that you can populate with you favourite hard drives as the need arises (and prices go down while capacity goes up), and uses a firmware or operating system that is as least proprietary as can be. In other words: avoid vendor lock-in, and watch out for expensive service contracts that have an unexpected effect on your ROI. Also be careful not to compare apples and oranges when reviewing populated, semi-populated, and fully populated NAS boxes. It might prove very useful to compare the price differences with what you would pay for the drives separately, keeping into account what they are expected to cost a few years down the road when you need the rest of them.

Granted, these systems get close to crossing the border with a SAN (Storage Area Network), but that’s a whole other story.

Pete Stevens

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