Disk enclosure

A 3.5-inch USB/FireWire hard disk enclosure with cover removed

A disk enclosure is a specialized casing 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 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 to retransmit data over connector and signal of a different standard.

Factory-assembled external hard disk drives, external DVD-ROM drives, and others consist of a storage device in a disk enclosures.

Benefits

An external hard drive enclosure that uses a 2.5-in drive and a USB connection for power and transfer

Key benefits to using external disk enclosures include:

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 enclosures. External 3.5-in floppy drives 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 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.

Simplified circuit diagrams of harddiskdrive enclosure.

Variants of caddy:[9]

Advantages:

Disadvantages:

Form factors

Factory-assembled Buffalo external hard drive in a disk enclosure

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 the term refers to a larger physical chassis. The term can be used both in reference to network-attached storage (NAS)[5] and components of a storage area network (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, temperature sensors, cooling systems, enclosure management devices, and redundant power supplies.

Connections

An eSATA and Mini USB hard disk enclosure board
Multiple connectors including external power on a 2.5 inch enclosure
The PCB of an enclosure controls the data transfer, generic mass storage device drivers are readily available on most operating systems
This 2.5 inch caddy uses a single connector mini USB

Native drive interfaces

SCSI, SAS, Fibre Channel, eSATAp, and eSATA interfaces can be used to directly connect the external hard drive to an internal host adapter, 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) and to use a more durable physical connector. A host adapter 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 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, 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 or NAS. Often, such drives are embedded computers running operating systems such as Linux or VxWorks 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.

See also

References

  1. "TiVo filling up? DVR expanders provide more room to record". Usatoday.Com. 2008-08-06. Retrieved 2009-07-29.
  2. "Connect a USB hard drive to the PS3 to backup content — Swapping the PS3 hard drive". Vgstrategies.about.com. 2009-06-16. Retrieved 2009-07-29.
  3. "Kingwin Big Drive RAID Enclosure Review". Virtual-Hideout. 2009-01-21. Retrieved 2009-07-29.
  4. 1 – (2006-10-30). "The CalDigit S2VR Duo RAID Enclosure : The 130 MB/s RAID Box For Video Or Storage — Review Tom's Hardware". Tomshardware.com. Retrieved 2009-07-29.
  5. 1 2 Venezia, Paul (2007-06-07). "Sun Fire X4500 server crams 48 drives into 4U | Storage". InfoWorld. Retrieved 2009-07-29.
  6. "Vizo Saturno One Touch Backup Enclosure Review :: Page 1 / 6". techPowerUp. Retrieved 2009-07-29.
  7. O'Brien, Bill (2005-10-18). "Review: Three One-Touch Backup Drives — Desktop Pipeline | Review: Three One-Touch Backup Drives". Informationweek.com. Retrieved 2009-07-29.
  8. Stevens, Tim (2009-01-13). "ioSafe announces Solo, the external, submersible, fire-proof HDD enclosure". Engadget.com. Retrieved 2009-07-29.
  9. Maris. "External Disk Enclosures and Caddies". HDDMag. Retrieved 30 June 2017.
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