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What is a solid-state drive?

A solid-state drive (SSD) is a semiconductor-based storage device, which typically uses NAND flash memory to save persistent data. Solid-state technology is transforming the storage with high speed flash memory.

Each NAND flash memory chip consists of an array of blocks, also known as a grid, and within each block, there is an array of memory cells, known as pages or sectors. The number of bits stored in each cell can vary, and they are typically categorized as either single-bit cells (i.e. "Single Level Cells" or "SLC"), 2- and 3-bit cells (i.e. "Multi-Level Cells/MLC" and "Triple-Level Cells/TLC"), or quad-bit cells ("QLC"). Each cell type also has its strengths and weaknesses. While SLCs are known for its reliability, high speeds and prices, QLCs have the advantage of being more affordable. Each grid can store between 256KB and 4MB. The central processing unit (CPU) acts as the controller for any reading or writing jobs to memory. Their size and low power requirements make them ideal for laptops, tablets, and smartphones.  

SSDs try to mimic HDDs through the use of nonvolatile solid-state memory, but they are much faster than the traditional hard drive or floppy disk.  HDDs have an inherent latency and access time caused by mechanical delays in the spinning of the platter and movement of the read/write head. Since SSDs have no moving parts, latency and time to access and store data is greatly reduced.

According to Gartner (link resides outside ibm.com), solid-state drives are emerging as the go-to storage platform to support structured data workloads, which is fueled by innovation around NAND flash and storage class memory (SCM) technology. They expect that by 2025 over 40% of all on-premises IT storage administration and support activities will be replaced by managed storage as a service, which is up from less than 5% in 2021.

Flash storage

Flash storage, also known as flash memory, is a type of solid-state technology which uses flash memory chips for writing and storing data. Flash storage solutions can range from USB drives to enterprise-level arrays. All-flash arrays are designed to maximize and speed up performance without the constraints of storage area network (SAN) legacy functions. They are more suitable for multi-cloud environments and storage protocols, like NVMe. Since most modern SSDs are flash-based, flash storage tends to be synonymous with a solid-state system. 

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Types of solid-state drives

As implied by the name, internal solid-state drives are installed inside a computer, directly connecting to its motherboard. External SSDs, on the other hand, are plugged in like external HDDs, frequently to USB 3.0 ports, and serve similar purposes. Internal SSDs connect via standard SATA, IDE, and m.2. while external SSDs utilize USB,  eSATA, and Thunderbolt connections.

There are two main types of SSD form factors: 

- mSATA III, SATA III, and traditional SSDs: While SATA SSDs are probably the most common, it is more of a legacy technology as it was designed with the intention of being installed in the place of a hard disk drive. That said, you may need a bay adapter or enclosure depending on your device, such as a desktop PC. While the ease of installation facilitated the adoption of SSDs, this interface is the process of phasing out with the introduction of PCIe and NVMe SSDs. By comparison, mSATA III, SATA III, and traditional SSDs are limited in their speed times, having a lower throughput compared to newer versions of SSDs in the market.

- PCIe and NVMe SSDs: Newer form factors, like U.2 and M.2 SSDs, utilize an interface protocol called, Nonvolatile Memory Express (NVMe), which was jointly developed by companies in the NVM express workgroup, such as Samsung, Intel, and Seagate. NVMe works with Peripheral Component Interconnect Express (a.k.a. PCI Express or PCIe) to deliver high data transfer speeds, reaching read speeds of over 3000 MB/s. The reduced latency makes this type of SSD ideal for gamers and their Playstations. These SSDs usually come with a heatsink to prevent overheating. 

Solid State Drives vs. Hard Disk Drives

IBM’s history with the hard drive dates all the way back to the 1950s with the IBM 650 RAMAC hard drive. Hard disk drives (HDD) use a spinning magnetic disk and a mechanical write head to manipulate data. The most common form factors are 2.5 and 3.5 inch drives, which are used for laptops and desktops, respectively.  While most HDDs leverage a SATA interface, also known as Serial ATA, you may also encounter Serial Attached SCSI (SAS) or Fibre Channel connections for specialized use. 

Unlike HDDs, solid-state drives (SSD) have no moving parts to slow them down, so SDDs are very appealing for their high throughput. However, solid-state users will tend to compromise on storage capacity. While high-capacity SSDs exist, users will pay a premium compared to HDDs. 

Many organizations are adopting a hybrid approach, mixing the speed of flash with the capacity of hard drives. A balanced infrastructure enables companies to apply the right technology for different storage needs, offering an economical way to transition from legacy HDDs without going entirely to flash.

Advantages and disadvantages of solid-state drives

- High Performance: Solid-state drives are more efficient in speed compared to hard drives due to its flash-based memory system, making it ideal for running apps, booting up your Windows or Mac OS, or transferring files. However, as storage capacity decreases, solid state drives can become increasingly slower. 

- Easy of Use: SDDs are easy to install, and they have no moving parts. Their size and weight also make them extremely portable, making them extremely appealing for popular mobile devices, like the Mac Book and iPad. 

- Durability and reliability: Thermal issues caused by high rotations per minute (RPM) and mechanical wear and tear cause deterioration and degradation in HDDs over time and create vulnerabilities to vibration, drops, and jolts.


- Limited number of writes: The main disadvantage of SSDs is that they have a limited lifetime number of writes. However, techniques, like wear leveling and overprovisioning, help enterprise class SSDs to withstand many years of continuous use.

- Cost: While the cost per storage unit (i.e. in gigabytes (GB) or terabytes (TB)) of SSDs is more expensive than HDDs, the energy usage of SSDs is lower. Unlike HDDs, SSDs do not have use up electricity to spin up disks from a standstill; its product design saves companies money on their energy bills. 

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