SSD Form Factors, NAND Flash Technologies and Interfaces

SSDs2018-10-25

Getting to Know the SSD Inside Out

In enterprise data centers and industrial environments where workload demands are high and the speed of data access is crucial, solid state drives (SSDs) are increasingly becoming the storage of choice.

What is an SSD? How can you choose the right SSD for your project to yield reduced total cost of ownership (TCO)? First, let us look under the hood and see what makes it work.

The Inside Story

An SSD and a hard disk drive (HDD) serve similar purposes— they are storage devices. Unlike an HDD, however, an SSD has no moving parts. It does not save data on magnetic platters, and there is no head rotating over the platters to read or locate data.

What is inside an SSD and how does it do what it is supposed to do?

Flash Controller

The flash controller is the heart and brains of the SSD. It is responsible for interfacing with the host computer and the other components of the SSD. When a host computer wants to send data to the SSD, the flash controller directs the flow of data to ensure its reliable storage and retrieval. It also contains the firmware that manages the SSD and performs background processes such as managing the flash file system, wear leveling, error correction, trim, and garbage collection.​​


Volatile Memory (DRAM Cache)

This is a small amount of memory that is used as temporary storage of data. It is not available in all SSDs. Because it is volatile, it requires power to retain information. Firmware in the controller decides when to flush or move the data from volatile (non-persistent) memory to the non-volatile (persistent) flash memory. In the event of an unexpected power loss, data in the cache could be lost or corrupted unless an effective power failure protection mechanism is available.


Non-Volatile NAND Flash Memory
Data is persistently stored in and retrieved from NAND flash memory chips. They are non-volatile because they retain data even when there is no power to the SSD.

Figure 1. Main components of an HDD and SSD. (Images are not to scale.) 

 

NAND Flash Memory Types

NAND flash memory is essentially categorized based on how much information each chip can store. Single level cell (SLC) stores only one bit of information on each cell. Multi-level cell (MLC) holds more than one bit of information, though it is commonly associated with two-bit memory. Triple level (TLC) and quad level (QLC) cells, as the names imply, store three and four bits respectively. For a comparison of the main NAND flash types, please click here.

On top of the standard types of NAND flash memory, ATP implements a new advanced firmware technology called "SLC Mode," which allows MLC flash to act as SLC at accessible price points without compromising performance, endurance, capacity and data retention. 

Beyond Conventional NAND Flash Labels

The more bits a cell can hold, the bigger the storage capacity. It is common to think that as more bits are crammed into a cell, error rates also increase, causing reliability and longevity to decrease. However, thanks to major headway in storage technology, people are no longer sticking to conventional labels. Economical options that were once relegated as mediocre choices can now have better performance, longer endurance and greater reliability due to powerful controllers, advanced firmware, robust error correction mechanisms, and meticulously screened components, along with stringent testing, validation and manufacturing practices.

ATP builds its products from the ground up, thoroughly screening components from the wafer and IC level to packaging and design all the way up to device/module level testing and validation, so customers can have peace of mind that only the choicest, premium products come out of ATP's manufacturing facilities. All ATP products are made for mission-critical applications where high levels of performance, reliability and endurance are required while maintaining low TCO and generating high returns on investment (ROI).

Getting Connected

An SSD connects to the host using an "interface," which adheres to a specific "protocol." Interface refers to the hardware transportation layer including voltage, current, and physical pin definition, while protocol refers to the set of rules, standards, command sets and drivers between the storage and the operating system. The choice ofinterface will determine the amount of data that can be transmitted within a period of time (bandwidth), the delay before data transfer actually begins after the transfer instruction is sent (latency) and the capability to expand the system or network to adapt to growing workloads (scalability). It will also determine whether your SSD will have hot-swap or hot-plug capabilities. All of these are important considerations in enterprise usage.

Briefly described below are commonly used SSD interfaces.

  • Serial ATA (SATA)
    SATA is currently the prevalent interface for connecting an SSD to the host. It affords the convenience of being used interchangeably with SATA-based HDDs. Transfer rates for first-generation SATA began at 1.5 Gb/s, and the latest generation, SATA revision 3.0, provides a native transfer rate of 6 Gb/s. SATA uses the Advanced Host Controller Interface (AHCI) command protocol, which was designed for slower mechanical drives with spinning disks.

  • PCI Express® (PCIe®)
    Though PCIe was originally designed as an interface for linking motherboard-mounted peripherals like graphics or wireless network cards, its excellent features for scalability, minimal latency, high bandwidth, and high performance makes it an emerging interface favorite, enabling SSDs to blaze past the SATA III limitation of 6 Gb/s transfers. The interface specification optimized for NAND flash and next-generation solid-state technologies is known as NVM Express® or NVMe. NVMe delivers twice the performance of SAS 12 Gb/s and four times the performance of SATA 6 Gb/s.

  • Serial Attached SCSI (SAS)
    SAS is designed for high-performance enterprise requirements and is backward compatible and interoperable with earlier SCSI technologies as well as SATA, so a SATA drive can be attached to a SAS port; however, a SAS drive cannot be plugged into a SATA port. SAS doubles the SATA transfer rate (up to 12 Gb/s), delivers better data integrity than SATA, and supports dual-port operation.

Form Follows Function

"Form factor" refers to the size and physical configuration of a device. Initially, SSDs were seen as HDD replacements and came in HDD sizes such as 1.8", 2.5", 3.5" and 5.25". In late 2010, SSDs consisting of flash chips and controllers attached to a circuit board were used in ultra-thin mobile computers. These SSDs were long, thin and narrow, and had no enclosure. Choosing the right form factor is important, as it defines whether it fits in the system chassis, how many can fit, and if it can be replaced without powering off the system (hot-plug/hot-swap functionality).

Below are typical SSD form factors available from ATP.

 

Form Factor

Description

Traditional HDD Sizes

SSDs with enclosure come in 1.8" for removable ultra-mobile applications, 2.5" and 3.5" for desktop and enterprise systems, and the less common 5.25" for special-purpose appliances like backup devices. ATP's 2.5" industrial SSDS with the SATA III 6 Gb/s interface are shock resistant and can operate in a wide range of temperatures, making them ideal for enterprise and industrial applications requiring outstanding performance, endurance and reliability amidst rigid operating conditions.

Solid State Modules


M.2 NVMe


M.2 SATA 2242, 2260 and 2280

Flash memory chips reside in a dual in-line memory module (DIMM) or similar form. They may use a standard HDD interface like SATA.

 

The M.2 standard provides higher performance and capacity while minimizing module footprint. M.2 modules connect either via SATA or PCIe, come in multiple widths and lengths, are available in soldered down or connectorized type, and can have single- or double-sided components. All soldered down modules are single-sided and are intended to be used in low-profile applications. (Note: M.2 modules are neither hot-swappable nor hot-pluggable.)

 

  • ATP M.2 NVMe SSDs fit into a PCIe 3.0 x4 slot, offer up to 1 TB capacity, and deliver a bandwidth of up to 32 Gb/s (8 Gb/s per lane), which is four to six times the data transfer speed of the previous-generation AHCI protocol on Serial ATA drives.

 

  • ATP M.2 SATA SSDs deliver high-performance SATA 6 Gb/s and adopt the double-sided configuration to enable higher densities. They come in three sizes: 2242, 2260 and 2280.

mSATA

Just roughly the size of a business card, an mSATA SSD adopts the PCI Express Mini form factor and connector. Though it can easily be mistaken for a PCIe mini card, an mSATA SSD signaling conforms to the mSATA standard, which is based on the SATA storage interface supporting maximum data transfer rates up to 6 Gb/s. It plugs into an existing PCIe Mini card slot but will function properly only if connected to a SATA host controller. Compatible slots will be labeled as either dedicated for mSATA or shared with PCIe mini. A PCIe Mini card installed on a dedicated mSATA slot will not function properly.

SlimSATA

Also called Half-Slim SATA, a SlimSATA SSD uses a 22-pin SATA pin connector, the same connector used on 2.5" SSDs. ATP SlimSATA SSDs are high-performance and reliable mass storage devices featuring an advanced wear-leveling algorithm for enhanced endurance.

 

Flash Memory Cards

Memory cards also use flash memory and are used either as removable or embedded storage. ATP's industrial flash memory cards are built for rigorous computing conditions in automotive applications and industrial environments. They feature advanced wear leveling and data integrity protection features and can withstand harsh operating environments with severe temperatures ranging from -40°C to 85°C. Flash memory cards in ATP's portfolio include SD/SDHC/SDXC, microSD/microSDHC/microSDXC, CFast, and CompactFlash (CF) cards.

Embedded USB (eUSB)

An embedded USB module complies with the Universal Serial Bus (USB) standards. It is commonly used as a boot drive for systems and applications. ATP eUSB modules are ideal for industrial and rugged environments. Advanced wear leveling ensures long usage life and ATP PowerProtector completes the last read/write operation during a sudden power loss event, so data is safely stored to the NAND flash.

USB Drives

A USB drive, also known as a USB stick, thumb drive, pen drive, or USB flash drive is a flash-based storage device that connects to the host via a USB interface. While commonly used as external removable storage, USB drives are now also being used in embedded industrial applications, mainly as boot drives. ATP Nanodura ruggedized industrial USB drives are suitable for mission-critical computing with their tough metal housing, which enables them to withstand extreme temperatures from -40°C to 85°C as well as resist water, moisture, dust, shocks, vibration, electrostatic discharge and other environmental strains.

Table 1. Common SSD form factors.

ATP Advantages

While it is common and helpful to choose SSD solutions based on NAND flash types, capacities and interfaces, endurance and reliability must also be considered to guarantee dependable operation over long periods of time. In industrial applications, devices often function under heavy workloads, extreme temperatures and harsh environments with dust, humidity and other external hazards. It is therefore important to go for a trusted manufacturer that takes control of every manufacturing process to ensure quality and steady supply.

As an established memory and storage manufacturer with over 25 years of expertise, ATP is committed to the highest quality of products and services. Here are our key differentiators

  • Strategic Partnerships ensure product longevity, supply stability, technical support, and smooth qualifications and transitions.

  • Process Ownership. ATP maintains complete control of its supply chains and takes charge of all stages of the manufacturing process from NAND characterization, wafer management, package-level validation and NAND flash screening all the way up to mass production.

  • NAND Self-Packaging Capability using high-quality Full-Grade ICs sourced 100% from Tier 1 manufacturers.

  • Rigorous Testing and Validation from IC to Module and MP Levels ensure the reliability of all flash products.

  • ATP-Owned Manufacturing Facilities with state-of-the-art production, testing and inspection equipment.

For detailed information on ATP industrial memory and storage solutions as well as testing, validation and manufacturing capabilities, visit the ATP website or contact an ATP Representative or Distributor in your area.

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