A NAS unit is essentially a self-contained computer connected to a network, with the sole purpose of supplying file-based data storage services to other devices on the network. The operating system and other software on the NAS unit provide the functionality of data storage, file systems, and access to files, and the management of these functionalities. The unit is not designed to carry out general-purpose computing tasks, although it may technically be possible to run other software on it.  NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often by connecting a browser to their network address.

RAID is an acronym first used in 1987 to describe a redundant array of inexpensive disks, a technology that allowed computer users to achieve high levels of storage reliability from low-cost and less reliable PC-class disk-drive components, via the technique of arranging the devices into arrays for redundancy. More recently, marketers representing industry RAID manufacturers reinvented the term to describe a redundant array of independent disks as a means of dissociating a "low cost" expectation from RAID technology.

"RAID" is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple hard disk drives. The different schemes/architectures are named by the word RAID followed by a number, as in RAID 0, RAID 1, etc.  RAID's various designs involve two key design goals: increase data reliability and/or increase input/output performance. When multiple physical disks are set up to use RAID technology, they are said to be in a RAID array. This array distributes data across multiple disks, but the array is seen by the computer user and operating system as one single disk.

A solid-state drive (SSD) is a data storage device that uses solid-state memory to store persistent data.  An SSD emulates a hard disk drive interface, thus easily replacing it in most applications.  An SSD using SRAM or DRAM (instead of flash memory) is often called a RAM-drive, not to be confused with a RAM disk.

The original usage of the term ‘solid-state’ refers to the use of semiconductor devices rather than electron tubes, but in this context, has been adopted to distinguish solid-state electronics from electromechanical devices as well. With no moving parts, solid-state drives are less fragile than hard disks and are also silent and as there are no mechanical delays, they usually enjoy very fast access times and latency.

In computing and optical recording, an optical disk is a flat, usually circular, disk which can contain audio, video or data encoded in microscopic pits (or bumps) on a special material (often aluminium) on one of its flat surfaces. The encoding material sits atop a thicker substrate (usually polycarbonate) which makes up the bulk of the disk and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disk surface and extending from the innermost track to the outermost track. The data is stored on the disk with a laser and can be accessed when the data path is illuminated with a laser diode in an optical disk drive which spins the disk at speeds of about 200 RPM up to 4000 RPM or more depending on the drive type, disk format, and the distance of the read head from the center of the disk (inner tracks are read at a faster disc speed). The pits or bumps distort the reflected laser light; hence most optical disks characteristically have an iridescent appearance created by the grooves of the reflective layer. This side of the disk contains the actual data and is typically coated with a transparent material, usually lacquer.

The Technologies

Today’s optical storage alternatives can be divided into two camps, UDO (Ultra Dense Optical) and Blu-Ray.

UDO

An Ultra Density Optical disc or UDO is a 133.35 mm (5.25") ISO cartridge optical disc which can store up to 60 GB of data utilising a design based on a Magneto-optical disc, but using Phase Change technology combined with a blue violet laser, a UDO disc can store substantially more data than a magneto-optical disc or MO, because of the shorter wavelength (405 nm) of the blue-violet laser employed. MOs use a 650 nm-wavelength red laser. Because its beam width is shorter when burning to a disc than a red-laser for MO, a blue-violet laser allows more information to be stored digitally in the same amount of space. Current generations of UDO store up to 60 GB, and a 120 GB version of UDO is in development.

Originally an optical disc storage medium developed as a replacement for the Magneto-optical disk, Ultra Density Optical was developed and announced by Sony on November 1 2000. It was later adopted with heavy investment by Plasmon, a UK technology company with extensive experience with computer archival backup systems and solutions and is now owned by a US company called Alliance Storage Technologies Inc (ASTI) based in Colorado, USA.

Currently UDO is being championed by its development partners ASTI/Plasmon, and Mitsubishi Chemical, parent company of the Verbatim media storage brand.

There are three versions of UDO: a True WORM (Write Once Read Many), an R/W (Re-Writable), and Compliant WORM (shreddable WORM).

BLU-RAY

Blu-ray Disc is an optical disc storage medium designed to supersede the standard DVD format. Its main uses are for storing high-definition video and data, with up to 25 GB per single layered, and 50 GB per dual layered disc. The disc has the same physical dimensions as standard DVDs and CDs. The name Blu-ray Disc derives from the blue-violet laser used to read the disc. While a standard DVD uses a 650 nanometer red laser, Blu-ray uses a shorter wavelength, a 405 nm blue-violet laser, and allows for almost six times more data storage than a DVD.

Blu-ray Disc was developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures.

The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD-size disc. The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85, and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot. This allows more information to be stored in the same area. For Blu-ray Disc, the spot size is 580 nm. In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding that further increase the capacity. All Blu-Ray Disc media is required to use hard-coating.

Although the Blu-ray Disc specification has been finalized, engineers continue to work on advancing the technology. Quad-layer (100 GB) discs have been demonstrated on a drive with standard, unaltered optics. In August 2006, TDK announced that they had created a working experimental Blu-ray Disc capable of holding 200 GB of data on a single side, using six 33 GB data layers. Its planned market launch is in the 2010–11 time frame

In December 2008, Pioneer Corporation unveiled a 400 GB Blu-ray Disc (containing 16 data layers, 25 GB each) that will be compatible with current players after a firmware update. Its planned market launch is in the 2012–13 time frame. Ongoing development is under way to create a 1 TB Blu-ray Disc as soon as 2015.

There is a popular misconception that "Data DeDuplication" and "Single Instance" are the same thing, they are not. Single instance is whereby an identical copy of a document is retained once for example an e-mail of 1MB is sent to 100 people, therefore you need to store the message once vs the normal way of 100x for the same sent message. As you can see single instance storage greatly reduces the amount of data stored on file servers and Email servers.

Data de-duplication on the other hand takes single instance storage one step further by looking at patterns of information within a "Data Block".

Storage virtualisation is the ability of IT managers to work with logical representation of physical storage. Using virtualisation, IT managers can see and manage data as a single logical resource, regardless of where it physically resides in the typical disparate group of storage systems and networks.