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A disk enclosure is a specialized casing designed to hold and power
disk drive Disk storage (also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is ...
s 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 In computer architecture, a bus (shortened form of the Latin '' omnibus'', and historically also called data highway or databus) is a communication system that transfers data between components inside a computer, or between computers. This e ...
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 complicated enough to require a separate
embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' ...
to retransmit data over connector and signal of a different standard. Factory-assembled external
hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...
s, external DVD-ROM drives, and others consist of a storage device in a disk enclosure.


Benefits

Key benefits to using external disk enclosures include: *Adding additional storage space and media types to small form factor and laptop computers, as well as sealed
embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' ...
s such as digital video recorders 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 may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...
or workstation than their chassis can hold. *Transferring data between non-networked computers, humorously known as
sneakernet Sneakernet, also called sneaker net, is an informal term for the transfer of electronic information by physically moving media such as magnetic tape, floppy disks, optical discs, USB flash drives or external hard drives between computers, rather ...
. *Adding an easily removable backup source with a separate power supply from the connected computer. *Using a
network-attached storage Network-attached storage (NAS) is a file-level (as opposed to block-level storage) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. The term "NAS" can refer to both the tech ...
-capable enclosure over a
network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...
to share data or provide a cheap off-site backup solution. *Preventing the
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
from a disk drive from increasing the heat inside an operating computer case. *Simple and cheap approach to
hot swapping Hot swapping is the replacement or addition of components to a computer system without stopping, shutting down, or rebooting the system; hot plugging describes the addition of components only. Components which have such functionality are said ...
. *Recovering the data from a damaged computer's hard drive, particularly when it does not 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 A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...
or optical disc drives inside
USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...
, FireWire, or Serial ATA enclosures. External 3.5-in
floppy drive A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
s are also fairly common, following a trend to not integrate floppy drives into compact and laptop 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 A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...
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 * some caddies do not require an external power supply, and instead obtain power from the device 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, SCSI and
SATA SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard t ...
drives and
USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...
, 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 SATA connectors * storage; typically larger than CDs,
DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind ...
s and
USB flash drive Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply ( interfacing) between computers, peripherals and other computers. A bro ...
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-in drives in hot-swappable drive caddies. * ''"5.25-inch" drive:'' (5.75 in × 8 in × 1.63 in = 146.1 mm × 203 mm × 41.4 mm)
Most desktop models of drives for optical 120-mm discs (
DVD-ROM The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind ...
or CD-ROM drives, CD or
DVD burner A DVD recorder is an optical disc recorder that uses optical disc recording technologies to digitally record analog or digital signals onto blank writable DVD media. Such devices are available as either installable drives for computers o ...
s), 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 floppy disks in the
IBM PC AT The IBM Personal Computer/AT (model 5170, abbreviated as IBM AT or PC/AT) was released in 1984 as the fourth model in the IBM Personal Computer line, following the IBM PC/XT and its IBM Portable PC variant. It was designed around the Intel 80 ...
. (The original "5.25-inch slot" in the IBM PC 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 × 5.75 in × 1 in = 101.6 mm × 146.05 mm × 25.4 mm)
This smaller, disk-drive form factor was introduced with the
Apple Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
series in 1984, and later adopted throughout the industry beginning widely with the
IBM PS/2 The Personal System/2 or PS/2 is IBM's second generation of personal computers. Released in 1987, it officially replaced the IBM PC, XT, AT, and PC Convertible in IBM's lineup. Many of the PS/2's innovations, such as the 16550 UART (serial p ...
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 threads: three on each side and four on the bottom. * ''"2.5-inch" drive:'' (2.75 in × 3.945 in × 0.374 in = 69.85 mm × 100.2 mm × 9.5 mm)
This even smaller, 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-in 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 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-inch 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 Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are consid ...
the term refers to a larger physical chassis. The term can be used both in reference to network-attached storage (NAS) and components of a
storage area network A storage area network (SAN) or storage network is a computer network which provides access to consolidated, block-level data storage. SANs are primarily used to access data storage devices, such as disk arrays and tape libraries from ser ...
(SAN) 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 A backplane (or "backplane system") is a group of electrical connectors 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 back ...
,
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...
sensors A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
, cooling systems, enclosure management devices, and redundant
power supplies A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a res ...
.


Connections


Native drive interfaces

SCSI, SAS, Fibre Channel,
eSATAp In computing, eSATAp (also known as Power over eSATA, Power eSATA, eSATA/USB Combo, eSATA USB Hybrid Port/EUHP) is a combination connection for external storage devices. An eSATA or USB device can be plugged into an eSATAp port. The socke ...
, and
eSATA SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard t ...
interfaces can be used to directly connect the external hard drive to an internal
host adapter In computer hardware, a host controller, host adapter, or host bus adapter (HBA), connects a computer system bus, which acts as the host system, to other network and storage devices. The terms are primarily used to refer to devices for conne ...
, without the need for any intervening controller. External variants of these native drive
protocols Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...
are extremely similar to the internal protocols, but are often expanded to carry power (such as eSATAp and the SCSI
Single Connector Attachment A SCSI connector ( ) is used to connect computer parts that use a system called SCSI to communicate with each other. Generally, two connectors, designated male and female, plug together to form a connection which allows two components, such as a ...
) and to use a more durable physical connector. A
host adapter In computer hardware, a host controller, host adapter, or host bus adapter (HBA), connects a computer system bus, which acts as the host system, to other network and storage devices. The terms are primarily used to refer to devices for conne ...
with external port may be necessary to connect a drive, if a computer lacks an available external port.


Direct attach serial interfaces

USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...
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 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 Internet Small Computer Systems Interface or iSCSI ( ) is an Internet Protocol-based storage networking standard for linking data storage facilities. iSCSI provides block-level access to storage devices by carrying SCSI commands over a TCP/IP ...
, NFS, or
CIFS Server Message Block (SMB) is a communication protocol originally developed in 1983 by Barry A. Feigenbaum at IBM and intended to provide shared access to files and printers across nodes on a network of systems running IBM's OS/2. It also provide ...
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 (NAS) is a file-level (as opposed to block-level storage) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. The term "NAS" can refer to both the tech ...
or NAS. Often, such drives are
embedded computer An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' as ...
s running operating systems such as
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, w ...
or
VxWorks VxWorks is a real-time operating system (or RTOS) developed as proprietary software by Wind River Systems, a wholly-owned subsidiary of Aptiv. First released in 1987, VxWorks is designed for use in embedded systems requiring real-time, determi ...
that use their NFS daemons and SAMBA 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.


Hard drive shucking

"Shucking" refers to the process of purchasing an external hard disk drive and removing the drive from its enclosure, in order for it to be used as an internal disk drive. This is performed because external drives are often cheaper than internal drives of the same capacity and model, and that external drives designed for continuous usage often contain hard drives designed for increased reliability. Following the hard disk drive shortages caused by the
2011 Thailand floods Severe flooding occurred during the 2011 monsoon season in Thailand. The flooding began at the end of July triggered by the landfall of Tropical Storm Nock-ten. These floods soon spread through the provinces of northern, northeastern, and centr ...
, data storage company Backblaze reduced its cost of acquiring hard drives by purchasing external hard drives and shucking them. According to Backblaze Chief Executive Gleb Budman, the company purchased 1,838 external drives during this period. Describing the process as "drive farming", the company noted that it was much cheaper for them to purchase 3 TB external drives and removing them from their cases manually, than it is to purchase internal drives.


See also

* Computer bus *
Computer case A computer case, also known as a computer chassis, is the enclosure that contains most of the hardware of a personal computer. The components housed inside the case (such as the CPU, motherboard, memory, mass storage devices, power supply unit a ...
*
External storage In computing, external storage refers to non-volatile (secondary) data storage outside a computer's own internal hardware, and thus can be readily disconnected and accessed elsewhere. Such storage devices may refer to removable media (e.g. pun ...
*
Hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...
*
Network-attached storage Network-attached storage (NAS) is a file-level (as opposed to block-level storage) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. The term "NAS" can refer to both the tech ...
*
Network Direct Attached Storage Network Direct Attached Storage (NDAS) is a proprietary storage area network system, originally marketed by the company Ximeta, for connecting external digital storage devices such as hard-disks, flash memory and tape drives via the Ethernet family ...
* SCSI Attached Fault-Tolerant Enclosure *
SCSI Enclosure Services SCSI Enclosure Services (SES) is a protocol for more modern SCSI enclosure products. An initiator can communicate with the enclosure using a specialized set of SCSI commands to access power, cooling, and other non-data characteristics. SES device ...
*
SGPIO Serial general purpose input/output (SGPIO) is a four-signal (or four-wire) bus used between a host bus adapter (HBA) and a backplane. Of the four signals, three are driven by the HBA and one by the backplane. Typically, the HBA is a storage con ...
- Serial General Purpose Input/Output *
Solid-state drive A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is a ...
*
USB Mass Storage Device The USB mass storage device class (also known as USB MSC or UMS) is a set of computing communications protocols, specifically a USB Device Class, defined by the USB Implementers Forum that makes a USB device accessible to a host computing device ...
*
USB flash drive Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply ( interfacing) between computers, peripherals and other computers. A bro ...


References

*
{{DEFAULTSORT:Disk Enclosure Computer storage devices
Enclosure Enclosure or Inclosure is a term, used in English landownership, that refers to the appropriation of "waste" or " common land" enclosing it and by doing so depriving commoners of their rights of access and privilege. Agreements to enclose land ...