2.1 Types of Storage Devices used in Storage Arrays

There are different types of storage devices which can be used for storing the data and based upon the business requirement & cost, storage devices are selected to be used in the storage system or storage array. There are three main types of media or storage devices which are currently used as a storage medium in the data centres.
  • Disk media
  • Solid-state media
  • Tape Media
Disk media refers to the electro-mechanical hard disk drive and most people refer to it as a disk drive, hard drive, or hard disk drive (HDD). Solid-state media refers to a flash memory–based storage or SSD, but other forms of solid-state media also exist. Tape media refers to magnetic tape to store the data. Below is the overview of the various storage media and we will discuss in deep about HDD & SSD in next posts.

Types of Storage Devices

Magnetic Tape:
A magnetic tape is a thin, long strip of plastic film that is coated with a magnetizable material, such as barium ferrite. The tape is packed in plastic cassettes and cartridges. A tape drive is the device to record and retrieve data on a magnetic tape. 

Magnetic TapeTape drives provide linear sequential read/write data access. A tape drive may be standalone or part of a tape library. Tape is a popular medium for long-term storage due to its relative low cost and portability. Tape drives are typically used by organizations to store large amounts of data, typically for backup, offsite archiving, and disaster recovery. 

The low access speed due to the sequential access mechanism, the lack of simultaneous access by multiple applications, and the degradation of the tape surface due to the continuous contact with the read/write head are some of the key limitations of tape.

Mechanical Disk Drive:
A magnetic disk is a circular storage medium made of non-magnetic material and coated with a ferromagnetic material. Data is stored on both surfaces of a magnetic disk by polarizing a portion of the disk surface. 

A disk drive is a device that comprises multiple rotating magnetic disks, called platters, stacked vertically inside a metal or plastic casing. Each platter has a rapidly moving arm to read from and write data to the disk. Disk drives are currently the most popular storage medium for storing and accessing data for performance-intensive applications. 

Disks support rapid access to random data locations and data can be written or retrieved quickly for a number of simultaneous users or applications. Disk drives use pre-defined protocols such as 
  • Advanced Technology Attachment (ATA)
  • Serial ATA (SATA)
  • Small Computer System Interface (SCSI)
  • Serial Attached SCSI (SAS)
  • Fibre Channel (FC)
These protocols reside on the disk interface controllers that are typically integrated with the disk drives. Each protocol has its unique performance, cost, and capacity characteristics.

Solid-State Drive (SSD):
A solid-state drive (SSD) uses semiconductor-based memory, such as NAND and NOR chips, to store data. SSDs, also known as “flash drives”, deliver the ultra-high performance required by performance-sensitive applications. 

Also Read: Solid State Drive (SSD) Overview

These devices, unlike conventional mechanical disk drives, contain no moving parts and therefore do not exhibit the latencies associated with read/write head movement and disk rotation. Compared to other available storage devices, SSDs deliver a relatively higher number of input/output operations per second (IOPS) with very low response times. 

They also consume less power and typically have a longer lifetime as compared to mechanical drives. However, flash drives do have the highest cost per gigabyte ratio.

Optical Disc
An optical disc is a flat, circular storage medium made of polycarbonate with one surface having a special, reflective coating such as aluminum. An optical disc drive uses a writing laser to record data on the disc in the form of microscopic light and dark dots. 

A reading laser reads the dots, and generates electrical signals representing the data. The common optical disc types are compact disc (CD), digital versatile disc (DVD), and Blu-ray disc (BD). These discs may be recordable or re-writable. 

Recordable or read-only memory (ROM) discs have Write Once and Read Many (WORM) capability and are typically used as a distribution medium for applications or as a means to transfer small amounts of data from one system to another. The limited capacity and speed of optical discs constrain their use as a general-purpose enterprise data storage solution. However, high-capacity optical discs are sometimes used as a storage solution for fixed-content and archival data. 

Hybrid Drives
Hybrid Drives are relatively new type of drives which are not commonly used in datacenters yet. This is the combination of the best of both mechanical drives and solid state drives. They have both a rotating platter and solid-state memory (flash). 

Also Read: What are Intelligent Storage Systems

Hybrid Dive
Most hybrid hard drives work on a simple caching technique. The most accessed sets of data will move from the spinning disk area to the solid-state area of the drive so that the data can be accessed much faster. But the drawback of this type of drives is when it comes to newly written data, newly written data is typically written to spinning disk first and then after a while of being frequently accessed, the data will move to solid-state memory. 

Some hybrid drives work in reverse fashion as well, the data is first written in solid-state area and then it will move down to mechanical disk area if not frequently accessed. However, both the approaches have their positive and negative feedbacks. 

Hybrid drives tries to bring both capacity and speed in single storage device and the inbuilt firmware will decide which data to move to solid-state area and which data goes into mechanical disk area. Hybrid drives are popular in personal desktop and computers but not commonly used in enterprise servers and storage arrays.

                                                Next: ElectroMechanical Hard Disk Drive (HDD) Overview
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