Definition

flash storage

This definition is part of our Essential Guide: Guide to managing data center costs and the IT budget
Contributor(s): Carol Sliwa and Matthew Haughn

Part of the storage hardware glossary:

Flash storage is any type of drive, repository or system that uses flash memory to keep data for an extended period of time.

Flash memory is ubiquitous in small computing devices and increasingly common in large business storage systems. The size and complexity of flash-based storage varies in devices ranging from portable USB drives, smartphones, cameras and embedded systems to enterprise-class all-flash arrays. Flash is packaged in a variety of formats for different storage purposes.

Flash storage uses and benefits

Flash memory is in wide use in consumer devices. Smartphones and MP3 players have largely abandoned the mechanical hard disk drive (HDD); flash provides advantages in compactness and power consumption. In notebook computers, flash storage offers the additional boon of being more resistant to the high gravitational acceleration bumps and drops these devices often receive in their mobile lives. This rugged nature allows the drives to maintain function through these events, which protects data. Flash is more prevalent in notebooks than desktop computers. Flash is also the standard form of storage in digital cameras, tablets and digital camcorders. Photolithographic shrinks and the development of denser types of flash have enabled an increase in capacity, making flash suitable for miniaturized applications.

Flash storage adoption is growing in enterprise storage systems. Initial deployments focused on the acceleration of I/O-intensive applications, such as databases and virtual desktop infrastructures. Use cases have since expanded to general enterprise workloads as the cost of flash has dropped and businesses have attempted to take advantage of its performance and low-latency benefits.

How does flash storage work?

Flash storage's memory is a form of EEPROM (electrically-erasable programmable read-only memory), although flash differs from conventional EEPROM in the way that it erases data. Flash erases whole blocks of data at a time, rather than on a bit-by-bit level, as conventional EEPROM does. A block stored on a flash memory chip must be erased before new data can be written to the microchip. Unlike dynamic RAM (DRAM), standard EEPROM and flash are nonvolatile memory. This means they do not require power to preserve stored data with integrity, so a system can be turned off -- or lose power -- without losing data.

Flash is solid-state storage, storing data using a charge on a capacitor to represent a bit. It is most often packaged in surface-mounted chips attached to a printed circuit board. There are no moving mechanical parts involved, which reduces power consumption. A typical serial ATA (SATA) flash drive consumes 50% or less of the power required by mechanical SATA HDDs, and may be capable of sequential read speeds of more than 500 megabytes per second in consumer drives -- faster than even the fastest enterprise-class mechanical HDDs. That is only a part of the picture because access times are where flash shines. Flash drives have no mechanical limitation for file access, which enables access times in microseconds, rather than the millisecond seek times required by mechanical HDDs -- which is several orders of magnitude less in latency.

Most flash storage systems are composed of memory chips and a flash controller. The memory chips store data while the controller manages access to the storage space on the memory unit. The flash controller is often multichannel, working with a RAM cache. The cache buffers the data going to and from a number of chips. Buffering enhances speed.

USB flash drive
The inside of a USB flash drive. On the left is the flash memory chip; the controller is on the right.

The history of flash storage

Dr. Fujio Masuoka is credited with inventing NOR and NAND flash, the two main types of flash memory, while he worked for Toshiba in the 1980s. In comparison to the slow process used by EEPROM, the new format's ability to be programmed and erased in large blocks reminded a colleague of Dr. Masuoka of a camera flash. NOR and NAND are named for the way the floating gates of the memory cells that hold data are interconnected in configurations that somewhat resemble a NOR or a NAND logic gate.

Intel's interest was piqued by the fact that NOR flash served as a higher functioning replacement for the EPROMs the company was shipping at that time. The company released the first NOR flash chips in 1988. Toshiba followed with the first NAND flash chips in 1989.

Major manufacturers of NAND flash memory chips include Intel, Micron Technology, Samsung, SK Hynix, Toshiba and Western Digital's SanDisk division. Major manufacturers of NOR flash memory include Cypress Semiconductor, Macronix, Microchip Technology, Micron Technology and Winbond.


The Computer History Museum's
video about the history of flash
memory.

Flash storage vs. traditional HDDs

NAND flash storage offers advantages over traditional hard disk drives. HDDs carry a lower cost per stored data bit, but flash drives can provide significantly higher performance, lower latency and reduce power consumption. The compact size also makes flash suitable for small consumer devices.

In enterprise systems, flash can enable a business to consolidate storage and lower the total cost of ownership. Fewer SSDs are needed to process transactions and deliver a comparable level of performance to systems using slower HDDs. Enterprises, in turn, can realize savings on rack space, system management, maintenance, and power and cooling costs. Data reduction technologies, such as inline deduplication and compression in all-flash storage systems, also enable businesses to reduce their data footprints.

As interest in flash storage has grown, industry watchers have noted a frequently overlooked caveat with flash. While speed and random read access is far superior in flash than in traditional hard drives, longevity may be reduced in heavy use with high write workloads. This reduction in endurance is due to flash's relatively limited tolerance for write-erase cycles. Manufacturers use features such as wear leveling and DRAM/nonvolatile RAM caching to provide flash storage with better performance while reducing flash SSD write wear to improve reliability.

Flash storage formats

NOR offers memory addressing on a byte scale, enabling true, random access and good read speeds. It was this addressability that interested Intel in NOR, since the technology matched the requirements for BIOS and extensible firmware interface (EFI) applications. NOR is more expensive per gigabyte (GB) than NAND because of its larger, individual cell size. NOR has slower write and erase times than NAND, as well. Both NAND and NOR use quantum tunneling of electrons to move electrons through the dielectric insulating material of the cell wall, which degrades the material over time. NOR flash is erasable, which makes it a great replacement for EEPROM- or ROM-based firmware BIOS and EFI chips where addressability and read speed is a boon, while the rewrite durability is less of a concern.

NAND offers greater write speeds than NOR flash along with a lower cost per GB. The lower cost is a result of the NAND memory cell's string design, saving die space and reducing the overall size of a chip per GB. NAND can come in single-level cell (SLC) and multi-level cell (MLC) forms, which include enterprise MLC (eMLC) and triple-level cell (TLC). SLC stores a single bit of information per cell. SLC generally offers greater speeds, especially when it comes to writes, greater longevity and fewer bit errors. MLC provides storage capacity for more data, as its cell is capable of more levels of charge (or states), which allow it to store multiple bits of data per cell. MLC can double capacity over SLC; TLC provides a third bit. The extra levels of charge, along with smarter flash controllers and firmware, can allow for bit error correction as well.

Solid-state storage comparison

Name

Description

Useful for

Conductive metal-oxide (CMOx)

A nonvolatile storage medium in which oxygen ions migrate between conductive and insulating metal-oxide layers within a single chip.

Emerging technology

Enterprise multi-level-cell (eMLC) flash

A form of multi-level cell (MLC) flash that offers an increased number of program/erase (PE) cycles for extended life and reliability.

Data storage for medium and large business high-performance computing.

Flash-based solid-state storage

Any data repository or system that uses flash memory. The size and complexity of such systems ranges from USB drives to enterprise-class, array-based memory systems.

Data storage for a wide variety of users and environments where performance is crucial.

Magnetoresistive random-access memory (MRAM)

A method of storing data bits using magnetic moments instead of the electrical charges used by DRAM and flash memory.

High-density, solid-state storage; emerging technology

Multi-level cell (MLC flash

An approach to flash memory in which two data bits can be written to the same cell, thereby doubling the storage capacity over single-level cell flash.

Used in standalone, hybrid and all-flash storage systems, spanning personal, small business and enterprise computing.

NAND flash memory

Flash memory technology or devices constructed using a cell topology that resembles NAND logic gates.

High-speed storage for all types of devices, including those for consumers (personal electronics), small businesses and enterprises.

NOR flash memory

Low-density, random-access flash memory technology or devices constructed using a cell topology that resembles NOR logic gates.

Typically used in mobile phones and personal electronics devices to store executable code.

Phase-change memory (PCM)

A form of computer RAM that stores data by altering the state of the matter rapidly back and forth between amorphous and crystalline on a microscopic scale.

An emerging technology noted for exceptional switching speed and high storage density.

RAM-based solid-state storage

A volatile, solid-state storage media based on DRAM technology that is significantly faster and more costly than NAND flash-based storage and that is insensitive to the number of PE cycles.

High-speed computer memory applications for business and government environments.

Resistive RAM (RRAM)

A form of nonvolatile storage that operates by changing the resistance of a specially formulated solid dielectric material.

An emerging technology noted for exceptional switching speed and high storage density.

Single-level cell (SLC) flash

A nonvolatile, solid-state storage device or technology that provides enhanced reliability and performance relative to MLC and eMLC flash media.

High-speed data storage for medium and large businesses and government agencies.

3D NAND flash

A type of flash memory in which cells are stacked vertically in layers to achieve higher density at a lower cost per bit.

The same types of consumer and business applications as 2D/planar NAND.

3D XPoint

A nonvolatile memory technology developed by Micron Technology and Intel offering higher performance, endurance and density than NAND flash.

Big data and transaction workloads requiring high performance and capacity.

Triple-level cell (TLC) flash

A type of NAND flash memory that stores three bits per cell, providing greater density, but lower endurance than SLC and MLC flash.

Mass storage for consumer applications; TLC 3D NAND is gaining adoption in enterprise systems for read-intensive workloads.

Flash storage interfaces

Flash storage for computer memory comes in a variety of interfaces, including USB, SAS, SATA, M.2 and PCI Express (PCIe). USB 3.1 Gen 2, known as SuperSpeed USB 10 Gbps, became available in 2013 and sees general use in flash drives, enclosures and mobile devices. SATA is a common format in desktops and notebook computers, and the 6 Gb version can eliminate bandwidth bottlenecks. Volume shipments of 12 Gbps SAS began in 2015. SAS-based SSDs are in wide use in enterprise storage systems. PCIe-connected flash storage provides sufficient bandwidth to allow for future expansion and represents the extreme end of speed-demanding offerings. Nonvolatile memory express technology in use with PCIe-based SSDs further reduces latency, increases IOPS and lowers power consumption through the streamlining of the I/O stack.

Flash in the data center

Data centers with I/O-intensive applications, such as high-transaction-rate databases and credit card processing systems, are increasingly turning to flash storage as an efficient and cost-effective way to increase throughput without having to add more servers. Major storage system manufacturers offer all-flash systems and hybrid arrays, which are equipped with SSDs and HDDs. Numerous all-flash storage specialists have also emerged to challenge the incumbents. Servers equipped with flash storage are also increasingly common and can further reduce latency.

Data center managers looking for ways to address the energy drain represented by HDDs are examining flash storage as a way to achieve green computing or green data center benchmarks. Flash SSDs provide high bandwidth at much lower power consumption than HDDs, making them a good choice for this application.

Flash for hobbyists

Many enthusiasts have adopted flash storage. These users often have their operating system, a few games and data-intensive applications such as audio, video and image editing software on a flash drive or even a flash RAID array. Main storage of files that don't require speed could be stored on a cost-effective and potentially massive conventional hard drive. Other enthusiasts may use all-flash, depending on whether they are excited about flash itself or its attributes, including silence, speed and the elimination of bottlenecks.

This was last updated in December 2016

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