SSD (solid-state drive, solid-state disk, solid-state storage drive)

This definition is part of our Essential Guide: Essential guide to desktop and laptop solid-state drives
Contributor(s): Andrew Burton

An SSD (solid-state drive or solid-state disk) is a nonvolatile storage device that stores persistent data on solid-state flash memory.

Solid-state drives actually aren't hard drives in the traditional sense of the term, as there are no moving parts involved. A traditional hard disk drive (HDD) consists of a spinning disk with a read/write head on a mechanical arm. An SSD, on the other hand, has an array of semiconductor memory organized as a disk drive, using integrated circuits (ICs) rather than magnetic or optical storage media.

Development and adoption of SSDs has been driven by a rapidly expanding need for higher input/output (I/O) performance. SSDs have much lower random access and read access latency than HDDs, making them ideal for both heavy read and random workloads. That lower latency is the direct result of the ability of flash SSD to read data directly and immediately from a specific flash SSD cell location. High-performance servers, laptops, desktops or any application that needs to deliver information in real-time or near real-time can benefit from solid-state drive technology.

SSD terminology

The following video offers advice on the most important things to consider before installing an SSD in your organization.

SSD form factors

The Solid State Storage Initiative (SSSI) has identified three major SSD form factors for the enterprise:

  • SSDs that come in traditional HDD form factors and fit into the same slots.
  • Solid-state cards that use standard card form factors, such as Peripheral Component Interconnect Express (PCIe), and reside on a printed circuit board (PCB).
  • Solid-state modules (SSMs) that reside in a Dual In-line Memory Module (DIMM) or small outline dual in-line memory module (SO-DIMM), and may use a standard HDD interface such as Serial Advanced Technology Attachment (SATA).

The following video discusses the wide range of solid-state storage form factors available today and some of the benefits and drawbacks of each.

SSD vs. HDD pros and cons

SSD performance is much faster than even the highest performance electromechanical disk drives. Seek time and latency are also substantially reduced and end users typically enjoy much faster boot times. In general, SSDs are more durable and much quieter than HDDs, with no moving parts to break or spin up/down. SSDs have a set life expectancy, as they have a finite number of write cycles before performance becomes erratic. This is not really a disadvantage per se, as HDDs degrade and eventually fail over time as well. In addition, SSDs employ wear leveling to increase drive lifespan. Wear leveling is typically managed by the flash controller, which uses an algorithm to arrange data so write/erase cycles are distributed evenly among all the blocks in the device.

The following video outlines some of the ideal workloads for SSD devices.

SSD pricing

Historically, SSD pricing has been much higher than that of conventional hard drives. Due to improvements in manufacturing technology and expanded chip capacity, SSD prices have dropped, allowing consumers and enterprise-level customers to re-evaluate SSDs as viable alternatives to conventional storage.

This was first published in October 2014

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