What is an SSD?
An SSD, or solid-state drive, is a type of storage device used in computers. This non-volatile storage media stores persistent data on solid-state flash memory. SSDs replace traditional hard disk drives (HDDs) in computers and perform the same basic functions as a hard drive. But SSDs are significantly faster in comparison. With an SSD, the device's operating system will boot up more rapidly, programs will load quicker and files can be saved faster. A traditional hard drive consists of a spinning disk with a read/write head on a mechanical arm called an actuator. An HDD reads and writes data magnetically. The magnetic properties, however, can lead to mechanical breakdowns.
By comparison, an SSD has no moving parts to break or spin up or down. The two key components in an SSD are the flash controller and NAND flash memory chips. This configuration is optimized to deliver high read/write performance for sequential and random data requests.
How do SSDs work?
An SSD reads and writes data to underlying interconnected flash memory chips made out of silicon. Manufacturers build SSDs by stacking chips in a grid to achieve different densities. SSDs read and write data to an underlying set of interconnected flash memory chips. These chips use floating gate transistors (FGTs) to hold an electrical charge, which enables the SSD to store data even when it is not connected to a power source. Each FGT contains a single bit of data, designated either as a 1 for a charged cell or a 0 if the cell has no electrical charge. Every block of data is accessible at a consistent speed. However, SSDs can only write to empty blocks. And although SSDs have tools to get around this, performance may still slow over time.
SSDs use three main types of memory: single-, multi- and triple-level cells. Single-level cells can hold one bit of data at a time -- a one or zero. Single-level cells (SLCs) are the most expensive form of SSD, but are also the fastest and most durable. Multi-level cells (MLCs) can hold two bits of data per cell and have a larger amount of storage space in the same amount of physical space as a SLC. However, MLCs have slower write speeds. Triple-level cells (TLCs) can hold three bits of data in a cell. Although TLCs are cheaper, they also have slower write speeds and are less durable than other memory types. TLC-based SSDs deliver more flash capacity and are less expensive than an MLC or SLC, albeit with a higher likelihood for bit rot due to having eight states within the cell.
What are the types of SSDs?
Types of SSDs include:
Solid-state drives: Basic SSDs deliver the least performance. SSDs are flash devices that connect via Serial Advanced Technology Attachment (SATA) or serial-attached SCSI (SAS) and provide a cost-effective first step into the solid-state world. For many environments, the performance boost in sequential read speeds from a SATA or SAS SSD will suffice.
PCIe-based flash: Peripheral Component Interconnect Express-based flash is the next step up in performance. While these devices typically offer greater throughput and more input/output operations per second, the biggest advantage is significantly lower latency. The downside is that most of these offerings require a custom driver and have limited built-in data protection.
Flash DIMMs: Flash dual in-line memory modules reduce latency, going further than PCIe flash cards by eliminating the potential PCIe bus contention. They require custom drivers unique to flash DIMMS, with specific changes to the read-only I/O system on the motherboard.
NVMe SSDs: These SSDs use the non-volatile memory express (NVMe) interface specification. This accelerates data transfer speeds between client systems and solid-state drives over a PCIe bus. NVMe SSDs are designed for high-performance non-volatile storage and are well-suited for highly demanding, compute-intensive settings.
NVMe-oF: The NVMe over Fabrics protocol enables data transfers between a host computer and a target solid-state storage device. NVMe-oF transfers data through methods such as Ethernet, Fibre Channel or InfiniBand.
Hybrid DRAM-flash storage: This dynamic random access memory (DRAM) channel configuration combines flash and server DRAM. These hybrid flash storage devices address the theoretical scaling limit of DRAM and are used to increase throughput between application software and storage.
What are the advantages of SSDs?
The benefits of SSDs over HDDs include:
Faster read/write speeds. SSDs can access large files quickly.
Quicker boot times and better performance. Because the drive does not need to spin up as an HDD would, it is more responsive and provides better load performance.
Durability. SSDs are more shock-resistant and can handle heat better than HDDs because they do not have moving parts.
Power consumption. SSDs need less power to operate than HDDs due to their lack of moving parts.
Quieter. SSDs produce less audible noise because there are no moving or spinning parts.
Size. SSDs come in a variety of form factors whereas HDD sizes are limited.
What are the disadvantages of SSDs?
Downsides that come with SSDs include:
Cost. SSDs are more expensive than traditional HDDs.
Life expectancy. Some SSDs, for example, those using NAND memory-flash chips, can only be written a specified number of times that is typically less than HDDs.
Performance. Limitations on the number of write cycles cause SSDs to decrease in performance over time.
Storage options. Because of cost, SSDs are typically sold in smaller sizes.
Data recovery. This time-consuming process can be expensive, as the data on damaged chips may not be recoverable.
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