Understanding SSD specifications

From 2.5-inch SATA drives to newer M.2 PCIe drives, SSDs (Solid State Drives) come in different shapes and sizes with different specifications. This article will take a closer look at these key specs to help users find the right type of SSD for their systems.

Form factors

One of the key specifications of an SSD is its form factor. The form factor is the storage drive’s size, shape and physical specifications, so it is important to consider the amount of physical space available in the server setup when choosing an SSD. The most common types of form factors are:

2.5-inch: The 2.5-inch form factor is commonly used for storage drives, from HDDs (Hard Disk Drives) to SSDs. In server infrastructures that already house traditional 2.5-inch HDDs, users can seamlessly swap out 2.5-inch SSDs into the 2.5-inch bays of existing infrastructures while making minimal changes. A larger form factor at 3.5-inch is also available for enterprise-grade SSDs.

M.2: The M.2 (a.k.a Next Generation Form Factor) form factor is a significantly more compact form factor than traditional 2.5” drives. The newer form factor is around the size of a stick of gum, which makes it ideal for setups with space constraints. M.2 SSDs have number designations to indicate the physical sizing of the drive. Take for example, a M.2 2230 SSD. The first two digits represent the width, and the latter two digits represent the length of the storage drive, so the 2230 SSD would be 22 mm in width and 30 mm in height.

Connector type

Another key specification to look at is the physical connector. Different types of motherboards will have different assortments of connectivity slots, so it is important to figure out which types of slots are available on the board before going forth with any SSD. The main types of physical connectors include:

SATA: The 22-pin SATA (Serial Advanced Technology Attachment) connector is ubiquitous on modern motherboards and is commonly used for traditional hard drives, so it should be a familiar connector type for users experienced with installing storage drives. Both 2.5” and 3.5” form factor SSDs use SATA connectors exclusively.

M.2: In addition to being a form factor, M.2 is also a type of physical connector used for storage drives. Newer motherboards are often designed with built-in M.2 slots. Unlike SATA storage drives, M.2 SSDs can be slotted directly into the motherboard without the need for connector cables. M.2 SSDs can utilize either SATA or PCIe interfaces, which will be explained in the following section. The distinction between the two types of M.2s is marked by the extra notch that is present on the SATA drive.

Interfaces:

The bus interface of the storage drive is responsible for communication between the storage device and the PC. As such, it plays a significant role in how efficiently the SSD can transfer data back and forth between the two. The most commonly used interfaces include:

SATA: SATA interfaces are faster than its predecessors because it uses a serial connection that does not require synchronicity of the data. Although even the slowest of SATA SSDs are faster than the fastest HDDs available on the markets, SATA SSDs have transfer speeds that are bottlenecked at around 500 Mbps, so they are often outmatched by newer counterparts. Both 2.5” and 3.5” SSDs also utilize the SATA interface.

PCle: The PCIe (Peripheral Component Interconnect Express) interface is a significant upgrade over the SATA interface. Whereas SATA is designed specifically as a storage interface, PCIe is an interface that connects directly with the CPU via PCIe lanes. It is used to link a wide assortment of components such as graphics cards, storage drives, and add-in cards. PCIe can deliver much faster transfer speeds than SATA at up to 1GB per second.

Communication Protocols

Communication protocols are essentially the “languages” that the bus interfaces utilize to communicate with the CPU. The types of communication protocols used by SSD interfaces include:

AHCI: The AHCI (Advanced Host Controller Interface) communication protocol is a slower, more outdated protocol that is used with SATA drives. AHCI is gradually being phased out in the SSD market by its newer, faster counterpart, NVMe.

NVMe: The terms PCIe and NVMe (Non-Volatile Memory Express) are often used interchangeably, but PCIe is a bus interface and NVMe is a communication protocol that works exclusively with PCIe. Compared to AHCI which was designed for traditional hard drives with mechanical moving parts, NVMe is designed specifically for storage drives and runs on top of the PCIe bus interface. NVMe requires less overhead from the CPU, meaning the CPU has to handle fewer tasks. NVMe also simplifies operations, reduces latency, and allows for significantly higher queue commands. With all of these features, NVMe optimizes the performance of PCIe SSDs.

Memory components

Modern SSDs utilize NAND (Not AND) flash memory to store data even when not connected to a power source. The types of NAND flash memory include:

SLC/MLC/TLC/QLC NAND: Currently, the SSD market offers single-level cell (SLC), multi-level cell (MLC), triple-level cell (TLC) and quad-layer cell (QLC) NAND flash SSDs. The naming refers to the number of bits per cell. SLC drives are the fastest and most durable at a single bit per cell but are also the most expensive. MLC solid-state are slower at double the bits per cell. TLC drives are the middle ground in terms of speed and pricing at three-bits per cell. QLC drives are the most cost-friendly but also the slowest and least durable at four bits per cell.

3D NAND: 3D NAND is a newer technology that differs from the 2D technology that is used on the aforementioned NAND drives. Unlike its predecessor, 3D NAND stacks memory cells vertically in multiple layers. This allows for higher storage density per bit, which improves storage performance. It also increases the storage drive’s durability and reduces power consumption, making it a significant upgrade over traditional 2D NAND storage drives.

Connect with Axiom

To summarize, popular SSDs can be generally categorized with the following specifications:

Drive Name 2.5” SATA 3.5” SATA M.2 SATA M.2 NVMe
Form Factor 2.5 3.5 M.2
Connector SATA M.2
Interface SATA PCIe
Protocol AHCI NVMe
Components NAND/3D NAND

Now that these specifications have been explained, users should have a clearer understanding of the differences between form factors, interfaces, and communication protocols.

Axiom is a leading provider of enterprise and client grade SSDs. To view our full lineup of OEM alternative SSDs, please visit: https://www.axiomupgrades.com/page/storage/. Contact an Axiom sales representative or visit our website for more details at https://www.axiomupgrades.com/

 

Sources:
1. https://www.snia.org/sites/default/files/SNIASSSIPCIe101WhitePaper_120314.pdf
2 https://www.snia.org/forums/cmsi/knowledge/formfactors
3 http://www.happysysadm.com/2011/07/solid-state-drives-some-theory-and.html
4 http://www.storagesearch.com/chartingtheriseofssds.html
5 https://www.snia.org/technology-focus-areas/physical-storage/nvme-ssd-classification

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