The development of science and technology promotes social changes, and the advancement of flash memory chip technology has triggered a surge in the solid-state drive (SSD) market. Its excellent performance and gradually reducing costs have made SSDs increasingly replace traditional mechanical hard drives (HDD) in the storage field. It also plays an increasingly important role in the embedded computing applications we are focusing on today.
Today, flash memory chips are also in a new transition, from 2D NAND to 3D NAND. By vertically stacking memory cells in multiple layers to achieve higher storage densities and faster read/write operations, this evolution is notable and quickly.
At first, SLC was considered the most advanced because of its durability and fast read and write speeds. Over the past decade in which MLC has dominated the industrial market for quite some time because it is cheaper, with larger capacity, and better meet the general market demand. Since 2018, 96-layer 3D (BiCS4) SSDs have become commonplace in the market. In 2020, NAND directly jumped from 96 layers to 128 layers, bringing greater application opportunities to the entire market.
Today we focus on discussing several key points in the selection of SSD for embedded computers, mainly from the working environment, hard disk capacity, erasing and writing cycles and so on.
As we all know, different equipment has different application fields, and different application fields have different surrounding environments, such as operating temperature, and some work indoors, with a temperature range of 0~70°C, while working outdoors may require considering
the subzero or high temperature factors. According to the current market division, it can be divided into -20~75℃, -40~85℃ and more extreme range -55~105℃.
In addition, factors such as air humidity , dust , oxidation, and vibration should also be considered.
Proper use of hard drives starts with looking at available capacity, however, inconsistent specifications make it a challenge.
SSD manufacturers may set the full flash capacity (that is, the actual flash capacity), while some manufacturers may only set part of the capacity and use the hidden remaining capacity as spare capacity, which we call over provisioning (OP). The OP approach uses the extra flash capacity to perform garbage collection to improve hard drive efficiency and extend SSD life.
For example, for an SSD with a capacity close to 256GB, manufacturer A specifies the full 256GB, while manufacturer B specifies 240GB, and manufacturer C specifies 200GB. The actual available capacity of the hard drive may be less than the stated capacity. A common reason is that a flash area is used for internal processing. Therefore, engineers should conduct tests under near-real field conditions to analyze SSD performance and life. Manufacturers usually classify hard drives as "industry" or "consumer". Compared with consumer-grade SSDs, industry-grade hard drives are often used in data centers or servers, which require larger flash capacity as a reserve to provide more stable performance over a longer period of time. Especially for storage arrays, engineers should ensure that their design maintains low latency during peak loads, so the choice of capacity is also important in practical applications.
When choosing an SSD, lifetime endurance and write performance endurance are important criterions, as the wrong choice can come with considerable costs. Endurance does not play a role when using an SSD as the boot medium, but is very important for application scenarios responsible for data logging tasks.
