Until recently most NAND flash relied on floating gate technologies, in which the electrons are trapped between two oxide layers in a region called the floating gate. Today’s NAND flash chips use either floating gate cells or charge trap cells. Each bit is registered as either charged (0) or not charged (1), providing the binary formula needed to represent the data.

A data bit is represented by an electrical charge state, which is determined by the electrons trapped between insulator layers within the cell. Inside the NAND CellĪ page is made up of multiple cells that each hold one or more data bits. This write/erase difference has serious consequences when updating data, as you’ll see later in the article. A kilobyte can equal 1000 bytes or 1024 bytes, depending on its usage.) Each time the SSD reads or writes data, it does so in 4-KiB chunks, but each time the drive erases data, it carries out a 256-KiB operation. Kibibytes are sometimes used instead of kilobytes because they’re more precise. In this case, each page is 4 kibibytes (KiB) and each block is 256 KiB, which equals 64 pages per block. Writing and erasing data in a NAND flash SSD (image by Dmitry Nosachev, licensed under Creative Commons Attribution-Share Alike 4.0 International) Data is read and written at the page level, but erased at the block level, as illustrated in Figure 1.įigure 1. Of these, the blocks and pages are the greatest concern, not because you configure or manipulate them directly, but because of how data is written, read, and erased on a NAND chip. A plane is divided into blocks, and a block is divided into pages. Each chip contains one or more dies, and each die contains one or more planes. Most contemporary SSDs are based on NAND flash, which is why it’s the focus of this article.Īn enterprise SSD contains multiple NAND flash chips for storing data. Although each offers advantages and disadvantages (a discussion beyond the scope of this article), NAND has emerged as the favored technology because it delivers faster erase and write times. Flash memory comes in two varieties: NOR and NAND. SSDs are based on flash memory technologies that enable data to be written, read, and erased multiple times. An HDD, however, uses magnetic media to store its data, whereas the SSD uses integrated electronic circuitry to retain specific charge states, which in turn map to the data bit patterns. Like an HDD, an SSD is a nonvolatile storage device that store data whether or not it is connected to power. You should think of this as an introduction not a complete treatise, a starting point for building a foundation in understanding the inner workings of your SSDs. To help with that process, this article introduces you to several important SSD concepts so you have a clearer picture of the components that go into an SSD and how they work together to provide reliable nonvolatile storage.īear in mind, however, that an SSD is a complex piece of technology and can easily justify much more in-depth coverage than what a single article can offer. The better you understand how SSDs operate, the more effectively you can select, deploy, and manage them in you organization. Concepts such as NAND chips, multi-level cells, and floating gate technologies can be somewhat daunting if you’re still thinking in terms of rotating disks and moving actuator arms, components that have no place in the SSD. They’ve also been dropping in price while supporting greater densities, making them suitable for a wide range of applications.ĭespite their increasing presence in the enterprise, there’s still a fair amount of confusion about how SSDs work and the features that distinguish one drive from another. SSDs are faster, smaller, use less energy, and include no moving parts. Solid-state drive (SSDs) have made significant inroads into enterprise data centers in recent years, supporting workloads once the exclusive domain of hard-disk drive (HDDs). Storage 101: Monitoring storage metrics.Storage 101: Convergence and Composability.Storage 101: Modern Storage Technologies.Storage 101: Data Center Storage Configurations.Storage 101: Understanding the NAND Flash Solid State Drive.Storage 101: Understanding the Hard-Disk Drive.Storage 101: Welcome to the Wonderful World of Storage.Storage 101: Understanding the NAND Flash Solid State Drive - Simple Talk Skip to content

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