Disk enclosure - AbsoluteAstronomy.com

A disk enclosure is essentially a specialized chassis

Chassis

A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...

designed to hold and power disk drives while providing a mechanism to allow them to communicate to one or more separate computers. Drive enclosures provide power to the drives therein and convert the data sent across their native data bus

Computer bus

In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...

into a format usable by an external connection on the computer to which it is connected. In some cases, the conversion is as trivial as carrying a signal between different connector types. In others, it is so complicated as to require a separate embedded system

Embedded system

An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...

to retransmit data over connector and signal of a different standard. Factory-assembled external hard disk drives, external DVD-ROM drives, and others are all built around disk enclosures. Bulkier models built around 2.5" and 3.5" hard drives and full-height 5.25" DVD-ROM drives use enclosures that are often nearly identical to OEM

Original Equipment Manufacturer

An original equipment manufacturer, or OEM, manufactures products or components that are purchased by a company and retailed under that purchasing company's brand name. OEM refers to the company that originally manufactured the product. When referring to automotive parts, OEM designates a...

enclosures.

Benefits

Key benefits to using external disk enclosures include:

Adding additional storage space and media types to small form factor
Small form factor
A small form factor is a computer form factor designed to minimize the volume of a desktop computer. For comparison purposes, the size of an SFF case is usually measured in litres. SFFs are available in a variety of sizes and shapes, including shoeboxes, cubes, and book-sized PCs...

and laptop
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...

computers, as well as sealed embedded system
Embedded system
An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...

s such as digital video recorder
Digital video recorder
A digital video recorder , sometimes referred to by the merchandising term personal video recorder , is a consumer electronics device or application software that records video in a digital format to a disk drive, USB flash drive, SD memory card or other local or networked mass storage device...

s and video game consoles.
Adding RAID capabilities to computers that lack RAID controllers or adequate space for additional drives.
Adding more drives to any given server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...

or workstation than their chassis can hold.
Transferring data between non-networked computers, humorously known as sneakernet
Sneakernet
Sneakernet is an informal term describing the transfer of electronic information, especially computer files, by physically couriering removable media such as magnetic tape, floppy disks, compact discs, USB flash drives, or external hard drives from one computer to another. This is usually in lieu...

.
Adding an easily removable backup source with a separate power supply from the connected computer.
Using a network-attached storage
Network-attached storage
Network-attached storage is file-level computer data storage connected to a computer network providing data access to heterogeneous clients. NAS not only operates as a file server, but is specialized for this task either by its hardware, software, or configuration of those elements...

-capable enclosure over a network to share data or provide a cheap off-site backup solution.
Preventing the heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

from a disk drive from increasing the heat inside an operating computer case.
Simple and cheap approach to hot swapping
Hot swapping
Hot swapping and hot plugging are terms used to describe the functions of replacing computer system components without shutting down the system...

.
Recovering the data from a damaged computer's hard drive, particularly when it doesn't share the same interface with the computer used to perform the recovery.
Lower the cost of removable storage by reusing hardware designed for internal use.
In some instances, provides a hardened chassis to prevent wear and tear.

Consumer enclosures

In the consumer market, commonly used configurations of drive enclosures utilize magnetic hard drives or optical disc drives inside USB, FireWire, or Serial ATA

Serial ATA

Serial ATA is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives...

enclosures. External 3.5" floppy drives are also fairly common, following a trend to not integrate floppy drives into compact and laptop

Laptop

A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...

computers. Pre-built external drives are available through all major manufacturers of hard drives, as well as several third-parties.

These may also be referred to as a caddy – a sheath, typically plastic or metallic, within which a hard disk drive can be placed and connected with the same type of adapters as a conventional motherboard and power supply would use. The exterior of the caddy typically has two female sockets, used for data transfer and power.

Variants of caddy:

some larger caddies can support several devices at once and can feature either separate outputs to connect each device to a different computer, or a single output to connect both over the same data cable
certain caddes don't require a power supply, instead depending for power on the computer to which they are connected
some caddies have integrated fans with which to keep the drives within at a cool temperature
caddies for all major standards exist, supporting for example ATA
AT Attachment
Parallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...

, SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...

and S-ATA drives and USB, SCSI and FireWire outputs

Advantages:

relatively high transfer speed; typically faster than other common portable media such as CDs, DVDs and USB flash drives, slower than drives connected using solely ATA, SCSI and S-ATA connectors
storage; typically larger than CDs, DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....

s and USB flash drive
USB flash drive
A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...

s
price-to-storage ratio; typically better than CDs, DVDs and USB flash drives

Disadvantages:

power; most variants require a supply, unlike CDs, DVDs and USB flash drives...
size; typically larger than CDs, DVDs and USB flash drives

Form factors

Multiple drives: RAID-enabled enclosures and iSCSI enclosures commonly hold multiple drives. High-end and server-oriented chassis are often built around 3.5" drives in hot-swappable drive caddies.

"5.25 inch" drive: (5.75 in x 8 in x 1.63 in = 146.1 mm x 203 mm x 41.4 mm)
Most desktop models of drives for optical 120-mm disks (DVD-ROM or CD-ROM
CD-ROM
A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....

drives, CD or DVD burners), are designed to be mounted into a so-called "5.25-inch slot", which obtained its nickname because this slot size was initially used by drives for 5.25 inches (133.4 mm) floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...

s in the IBM PC AT. (The original "5.25-inch slot" in the IBM PC
IBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...

was with 3.25 in (82.6 mm) twice as high as the one commonly used today; in fact, the PC's drive size was called "5.25 inch full-height", and the size used in the PC AT and commonly used today is "5.25 inch half-height".)

"3.5 inch" drive: (4 in x 5.75 in x 1 in = 101.6 mm x 146.05 mm x 25.4 mm)
This smaller, 4 inches (101.6 mm) disk-drive form factor was introduced with the Apple Macintosh series in 1984, and later adopted throughout the industry beginning widely with the IBM PS/2 series in 1987, which included drives of this size for 90-mm ("3.5-inch") floppy disks. This form factor is today used by most desktop hard drives. They usually have 10 mounting holes with American 6-32 UNC 2B
Unified Thread Standard
The Unified Thread Standard defines a standard thread form and series—along with allowances, tolerances, and designations—for screw threads commonly used in the United States and Canada...

threads: three on each side and four on the bottom.

"2.5 inch" drive: (2.75 in x 3.945 in x 0.374 in = 69.85 mm x 100.2 mm x 9.5 mm)
This even smaller, 2.75 inches (69.9 mm) form factor is widely used today in notebook computers and similar small-footprint devices. One commonplace feature for these drives is radically lower power consumption than is found in larger drives. This enables enclosure vendors to power the devices directly from the host device's USB or other external bus, in most cases.

"1.8 inch" drive: Found in extremely compact devices, such as certain portable media players and smaller notebooks, these devices are not standardized like their 2.5 inch cousins.

A range of other form factors has emerged for mobile devices. While laptop hard drives are today generally of the 9.5 mm high variant of the "2.5 inch" drive form factor, older laptops and notebooks had hard drives that varied in height, which can make it difficult to find a well-fitting chassis. Laptop optical drives require "slim" 5.25" enclosures, since they have approximately half the thickness of their desktop counterparts, and most models use a special 50-pin connector that differs from the 40-pin connectors used on desktop ATA

AT Attachment

Parallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...

drives.

While they are less common now than they once were, it is also possible to purchase a drive chassis and mount that will convert a 3.5" hard drive into a removable hard disk that can be plugged into and removed from a mounting bracket permanently installed in a desktop PC case. The mounting bracket carries the data bus and power connections over a proprietary connector, and converts back into the drive's native data bus format and power connections inside the drive's chassis.

Enterprise enclosures

In enterprise storage

Enterprise storage

In computing, an enterprise storage is the computer storage designed for large-scale, high-technology environments of the modern enterprises. When comparing to the consumer storage, it has higher scalability, higher reliability, better fault tolerance, and much higher initial price.From the...

the term refers to a larger physical chassis. The term can be used both in reference to network-attached storage and components of a storage area network

Storage area network

A storage area network is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices...

or be used to describe a chassis directly attached to one or more servers over an external bus. Like their conventional server brethren, these devices may include a backplane

Backplane

A backplane is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete...

, temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

sensors, enclosure management devices, and redundant power supplies.

Connections

Native drive interfaces

SCSI

Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...

, SAS

Serial Attached SCSI

Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...

, Fibre Channel

Fibre Channel

Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...

, eSATAp

ESATAp

In computing, eSATAp is a high speed connection for external storage devices. It is a combination of serial port connectors into which an eSATAp, eSATA or USB devices can be plugged...

, and eSATA

Sata

Sata is a traditional dish from the Malaysian state of Terengganu, consisting of spiced fish meat wrapped in banana leaves and cooked on a grill.It is a type of Malaysian fish cake, or otak-otak...

interfaces can be used to directly connect the external hard drive to an internal host adapter

Host adapter

In computer hardware, a host controller, host adapter, or host bus adapter connects a host system to other network and storage devices...

, without the need for any intervening controller. External variants of these native drive protocols are extremely similar to the internal protocols, but are often expanded to carry power (such as eSATAp and the SCSI Single Connector Attachment

Single Connector Attachment

Single Connector Attachment, or SCA, is a type of connection for the internal cabling of SCSI systems. There are two versions of this connector: the SCA-1, which is deprecated, and SCA-2, which is currently in use in most systems...

) and to use a more durable physical connector. A host adapter

Host adapter

In computer hardware, a host controller, host adapter, or host bus adapter connects a host system to other network and storage devices...

with external port may be necessary to connect a drive, if a computer lacks an available external port.

Direct attach serial interfaces

USB or FireWire connections are typically used to attach consumer class external hard drives to a computer. Unlike SCSI, eSATA, or SAS these require circuitry to convert the hard disk's native signal to the appropriate protocol. Parallel ATA

AT Attachment

and internal Serial ATA hard disks are frequently connected to such chassis because nearly all computers on the market today have USB or FireWire ports, and these chassis are inexpensive and easy to find.

Network protocols

iSCSI

ISCSI

In computing, iSCSI , is an abbreviation of Internet Small Computer System Interface, an Internet Protocol -based storage networking standard for linking data storage facilities. By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage...

, NFS, or CIFS are all commonly used protocols that are used to allow an external hard drive to use a network to send data to a computer system. This type of external hard drive is also known as Network-attached storage

Network-attached storage

Network-attached storage is file-level computer data storage connected to a computer network providing data access to heterogeneous clients. NAS not only operates as a file server, but is specialized for this task either by its hardware, software, or configuration of those elements...

or NAS. Often, such drives are embedded computers running operating systems such as Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

or VxWorks

VxWorks

VxWorks is a real-time operating system developed as proprietary software by Wind River Systems of Alameda, California, USA. First released in 1987, VxWorks is designed for use in embedded systems.- History :...

that use their NFS daemons and SAMBA

Samba

Samba is a Brazilian dance and musical genre originating in Bahia and with its roots in Brazil and Africa via the West African slave trade and African religious traditions. It is recognized around the world as a symbol of Brazil and the Brazilian Carnival...

to provide a networked file system. A newer technology NAS, has been applied to some disk enclosures, which allows network ability, direct connection (e.g. USB) and even RAID features.