Solid-state storage

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Solid-state storage (SSS) is non-volatile computer storage that has no moving parts; it uses only electronic circuits. This solid-state design dramatically differs from the commonly-used competing technology of electromechanical magnetic storage which uses moving media coated with magnetic material. [1] [2] Generally, SSS is much faster but more expensive for the same amount of storage. [3] [4] [5]

Contents

SSS devices typically use flash memory, but some use battery-backed random-access memory (RAM). Devices come in various types, form factors, storage sizes, and interfacing options to satisfy application requirements for many computer systems and appliances. [4]

Overview

Historically, computer system secondary storage has been implemented to leverage magnetic properties of surface coatings applied to rotating platters (in hard disk drives and floppy disks) or linearly moving strips of plastic film (in tape drives). Pairing such magnetic media with read/write heads allows data to be written by separately magnetizing small sections of the ferromagnetic coating, and read later by detecting the transitions in magnetization. For the data to be read or written, exact sections of the magnetic media need to pass under the read/write heads that flow closely to the media surface; as a result, reading or writing data imposes delays required for the positioning of magnetic media and heads, with the delays differing depending on the actual technology. [6]

An illustration of the write amplification phenomenon in flash-based storage devices NAND Flash Pages and Blocks.svg
An illustration of the write amplification phenomenon in flash-based storage devices

Over time, advancements in central processing unit (CPU) speed has driven innovation in secondary storage technology. [7] One such innovation, flash memory, is a non-volatile storage medium that can be electrically erased and reprogrammed.

Solid-state storage typically uses the NAND type of flash memory, which can be accessed in chunks smaller than the entire capacity of the device. The minimal chunk size (page) for a read operation is much smaller than the minimal chunk size (block) for a write/erase operation, resulting in an undesirable phenomenon called write amplification that limits the random write performance and write endurance of a flash-based storage device.

Some solid-state storage devices use (volatile) RAM and a battery that preserves the contents of the RAM without system power as long as the battery continues to provide power. Flash-based storage does not suffer the limitation of a battery, but RAM-backed storage is faster and does not experience write amplification. [3] [8] [9]

As a result of having no moving mechanical parts, solid-state storage has no data access latency required to move the media as in an electromechanical storage device. This allows for significantly higher I/O operation rates (IOPS). Additionally, solid-state storage consumes less power, has better physical shock resistance, and produces less heat and no vibration.

Compared to electromechanical, solid-state devices tend to cost more for the same capacity, and generally are not available in the larger capacities available for electromechanical.

Also, flash-based devices experience memory wear that reduces service life resulting from limitations of flash memory that impose a finite number of program–erase cycles used to write data. Due to this, solid-state storage is frequently used for hybrid drives, in which solid-state storage serves as a cache for frequently accessed data instead of being a complete substitute for traditional secondary storage. [4] [5] [10]

Device types

Intel DC S3700 SSD series, top side of a 100 GB SATA 3.0 model.jpg
An SSD, in form of a 2.5-inch bay device that uses Serial ATA (SATA) interface
SD CARD moteur et stockage.jpg
Internals of an SD card, showing the flash memory and controller integrated circuits

A solid-state drive (SSD) provides secondary storage for relatively complex systems including personal computers, embedded systems, portable devices, large servers and network-attached storage (NAS). To satisfy such a wide range of uses, SSDs are produced with various features, capacities, interfaces and physical sizes and layouts. [4]

Solid-state storage is also available as removable media. A memory card, such as MMC and SD, is shaped to fit into a special port for the card. A USB flash drive connects via USB and is not constrained by shape and size as a card is. [2] [11]

In general, an SSD uses a relatively fast interface such as Serial ATA (SATA) or PCI Express (PCIe) paired with a logical device interface such as AHCI or NVM Express (NVMe). Removable devices use simpler, slower interfaces such as the one-bit SD interface or SPI. [12] [13]

See also

Related Research Articles

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Computer data storage or digital data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.

<span class="mw-page-title-main">Hard disk drive</span> Electro-mechanical data storage device

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 magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data when powered off. Modern HDDs are typically in the form of a small rectangular box.

<span class="mw-page-title-main">Flash memory</span> Electronic non-volatile computer storage device

Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both use the same cell design, consisting of floating gate MOSFETs. They differ at the circuit level depending on whether the state of the bit line or word lines is pulled high or low: in NAND flash, the relationship between the bit line and the word lines resembles a NAND gate; in NOR flash, it resembles a NOR gate.

A RAM drive is a block of random-access memory that a computer's software is treating as if the memory were a disk drive. RAM drives provide high-performance temporary storage for demanding tasks and protect non-volatile storage devices from wearing down, since RAM is not prone to wear from writing, unlike non-volatile flash memory. They are in a sense the reverse of virtual memory: RAM drive uses a volatile fast memory as if it's a nonvolatile slow memory. Virtual memory is the opposite.

<span class="mw-page-title-main">CompactFlash</span> Memory card format

CompactFlash (CF) is a flash memory mass storage device used mainly in portable electronic devices. The format was specified and the devices were first manufactured by SanDisk in 1994.

Wear leveling is a technique for prolonging the service life of some kinds of erasable computer storage media, such as flash memory, which is used in solid-state drives (SSDs) and USB flash drives, and phase-change memory. There are several wear leveling mechanisms that provide varying levels of longevity enhancement in such memory systems.

In computing, a removable media is a data storage media that is designed to be readily inserted and removed from a system. Most early removable media, such as floppy disks and optical discs, require a dedicated read/write device to be installed in the computer, while others, such as USB flash drives, are plug-and-play with all the hardware required to read them built into the device, so only need a driver software to be installed in order to communicate with the device. Some removable media readers/drives are integrated into the computer case, while others are standalone devices that need to be additionally installed or connected.

<span class="mw-page-title-main">USB flash drive</span> Data storage device

A flash drive is a data storage device that includes flash memory with an integrated USB interface. A typical USB drive is removable, rewritable, and smaller than an optical disc, and usually weighs less than 30 g (1 oz). Since first offered for sale in late 2000, the storage capacities of USB drives range from 8 to 256 gigabytes (GB), 512 GB and 1 terabyte (TB). As of 2023, 2 TB flash drives were the largest currently in production. Some allow up to 100,000 write/erase cycles, depending on the exact type of memory chip used, and are thought to physically last between 10 and 100 years under normal circumstances.

Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.

Data remanence is the residual representation of digital data that remains even after attempts have been made to remove or erase the data. This residue may result from data being left intact by a nominal file deletion operation, by reformatting of storage media that does not remove data previously written to the media, or through physical properties of the storage media that allow previously written data to be recovered. Data remanence may make inadvertent disclosure of sensitive information possible should the storage media be released into an uncontrolled environment.

<span class="mw-page-title-main">USB mass storage device class</span> USB device class for drives

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In computing, a hybrid drive is a logical or physical storage device that combines a faster storage medium such as solid-state drive (SSD) with a higher-capacity hard disk drive (HDD). The intent is adding some of the speed of SSDs to the cost-effective storage capacity of traditional HDDs. The purpose of the SSD in a hybrid drive is to act as a cache for the data stored on the HDD, improving the overall performance by keeping copies of the most frequently used data on the faster SSD drive.

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, compact flash drives, portable storage devices, or network-attached storage. Web-based cloud storage is the latest technology for external storage.

<span class="mw-page-title-main">ReadyBoost</span> Disk caching component of Microsoft Windows

ReadyBoost is a disk caching software component developed by Microsoft for Windows Vista and included in later versions of Windows. ReadyBoost enables NAND memory mass storage CompactFlash, SD card, and USB flash drive devices to be used as a cache between the hard drive and random access memory in an effort to increase computing performance. ReadyBoost relies on the SuperFetch and also adjusts its cache based on user activity. ReadyDrive for hybrid drives is implemented in a manner similar to ReadyBoost.

<span class="mw-page-title-main">Solid-state drive</span> Computer storage device with no moving parts

A solid-state drive (SSD) is a solid-state storage device. It provides persistent data storage using no moving parts. It is sometimes called semiconductor storage device or solid-state device. It is also called solid-state disk because it is frequently interfaced to a host system in the same manner as a hard disk drive (HDD).

<span class="mw-page-title-main">Read-only memory</span> Electronic memory that cannot be changed

Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing software that is rarely changed during the life of the system, also known as firmware. Software applications, such as video games, for programmable devices can be distributed as plug-in cartridges containing ROM.

This glossary of computer hardware terms is a list of definitions of terms and concepts related to computer hardware, i.e. the physical and structural components of computers, architectural issues, and peripheral devices.

<span class="mw-page-title-main">Flash memory controller</span> Integrated circuit that interfaces flash memory to a host like a PC

A flash memory controller manages data stored on flash memory and communicates with a computer or electronic device. Flash memory controllers can be designed for operating in low duty-cycle environments like memory cards, or other similar media for use in PDAs, mobile phones, etc. USB flash drives use flash memory controllers designed to communicate with personal computers through the USB port at a low duty-cycle. Flash controllers can also be designed for higher duty-cycle environments like solid-state drives (SSD) used as data storage for laptop computer systems up to mission-critical enterprise storage arrays.

NVM Express (NVMe) or Non-Volatile Memory Host Controller Interface Specification (NVMHCIS) is an open, logical-device interface specification for accessing a computer's non-volatile storage media usually attached via the PCI Express bus. The initial NVM stands for non-volatile memory, which is often NAND flash memory that comes in several physical form factors, including solid-state drives (SSDs), PCIe add-in cards, and M.2 cards, the successor to mSATA cards. NVM Express, as a logical-device interface, has been designed to capitalize on the low latency and internal parallelism of solid-state storage devices.

An open-channel solid state drive is a solid-state drive which does not have a firmware Flash Translation Layer implemented on the device, but instead leaves the management of the physical solid-state storage to the computer's operating system. The Linux 4.4 kernel is an example of an operating system kernel that supports open-channel SSDs which follow the NVM Express specification. The interface used by the operating system to access open-channel solid state drives is called LightNVM.

References

  1. ↑ "What is Solid-State Storage (SSS)?". techopedia.com. Retrieved July 11, 2015.
  2. 1 2 "Backing Storage: Optical and Solid State". jhigh.co.uk. August 30, 2011. Retrieved July 11, 2015.
  3. 1 2 Margaret Rouse; Brien Posey. "Solid-state storage definition". techtarget.com. Retrieved July 11, 2015.
  4. 1 2 3 4 Michael Singer (January 7, 2013). "Solid State Storage Is Taking Over The Datacenter – Slowly". readwrite.com. Retrieved July 11, 2015.
  5. 1 2 Jonathan Corbet (October 4, 2010). "Solid-state storage devices and the block layer". LWN.net . Retrieved July 11, 2015.
  6. ↑ "Red Hat Enterprise Linux 3: Introduction to System Administration, Chapter 5. Managing Storage". Red Hat. November 2, 2013. Archived from the original on 2016-03-21. Retrieved July 11, 2015.
  7. ↑ "Accelerating Financial Applications Using Solid State Storage" (PDF). LSI Corporation. November 2011. pp. 1–2. Retrieved July 11, 2015.
  8. ↑ Chris Evans (November 2014). "Flash storage 101: How solid state storage works". computerweekly.com. Retrieved July 11, 2015.
  9. ↑ Xiao-yu Hu; Evangelos Eleftheriou; Robert Haas; Ilias Iliadis; Roman Pletka (2009). "Write Amplification Analysis in Flash-Based Solid State Drives". CiteSeerX   10.1.1.154.8668 .
  10. ↑ Joel Santo Domingo (February 17, 2015). "SSD vs. HDD: What's the Difference?". pcmag.com. Retrieved July 11, 2015.
  11. ↑ "Solid-State Storage Devices". igcseict.info. April 25, 2015. Retrieved July 11, 2015.
  12. ↑ Chris Hoffman (September 19, 2014). "eMMC vs. SSD: Not All Solid-State Storage is Equal". howtogeek.com. Retrieved July 11, 2015.
  13. ↑ "PCIe SSD: What it is and how you can use it". computerweekly.com. June 2010. Retrieved July 11, 2015.
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