When your friend recommends an “incredibly cheap” SSD, don’t just focus on the price — ask, “What type of NAND flash chips does it use?” Just like checking the origin and variety when buying fruits and vegetables, the NAND flash chips in an SSD truly determine how long it will last, how fast it runs, and how stable its performance is.
For SSD-based M.2 modules, the most common sizes are 22mm (width) x 30mm (length), 22mm x 42mm, 22mm x 60mm, 22mm x 80mm, and 22mm x 110mm. The card naming corresponds to these dimensions:
The first two digits define the width (all are 22mm), and the remaining digits define the length, ranging from 30mm to 110mm. Therefore, M.2 SSD specifications include 2230, 2242, 2260, 2280, and 22110.
This is common with flash storage devices—whether internal SSDs or external USB drives—partly due to the difference in how flash memory and traditional spinning hard drive manufacturers calculate megabytes. HDD manufacturers calculate a megabyte (or 1,000 x 1,000 bytes) as 1,000KB, while flash-based storage uses binary calculations, where 1MB equals 1,024KB.
Example: For a 1TB flash memory storage device, Windows will report the available capacity as 931.32GB. (1,000,000,000,000 ÷ 1,024 ÷ 1,024 ÷ 1,024 = 931.32GB).
Additionally, operating systems reserve some storage space for formatting and other functions, such as firmware and/or controller-specific information, so a portion of the stated capacity is not available for user data storage.
M.2 was developed by the standards organizations PCI-SIG and SATA-IO, and defined in the PCI-SIG M.2 and SATA Revision 3.2 specifications. It was originally called Next Generation Form Factor (NGFF), and was officially renamed to M.2 in 2013. Many people still refer to M.2 as NGFF.
The compact M.2 form factor is suitable for many types of plug-in cards, such as Wi-Fi, Bluetooth, satellite navigation, Near Field Communication (NFC),
wireless radio (WiGig), Wireless Gigabit Alliance (WWAN), wireless wide area network (WWAN), and solid-state drives (SSDs). M.2 has a form factor specifically designed for SSDs.
Solid State Drives (SSDs) come in various form factors and protocols. The first generation SSDs were 2.5-inch form factor using SATA interface and AHCI protocol, which are standards originally designed for mechanical hard drives, allowing easy upgrades from HDDs to SSDs. Later, the native flash storage protocol NVMe emerged, enabling faster transfer speeds and is applied in some of the latest high-end PCs and laptops. All NVMe SSDs use M.2, U.2, or AIC PCIe interfaces. SATA 2.5-inch SSDs have been available for a while and are still used in many computers today. Learn more about the differences between NVMe and SATA.
S.M.A.R.T., or SMART, stands for Self-Monitoring, Analysis, and Reporting Technology. SMART is a system used to monitor storage devices, collecting health data from the drive and reporting it to users. It is very useful for ensuring your drive operates in optimal condition. Learn about the history of SMART and how it has evolved to adapt to solid-state drives.
Originally, SMART was a method used by disk drive manufacturers to report the health status of hard disk drives (HDDs) to computers. Although some parameters were listed, each manufacturer could freely choose which parameters to include and what thresholds to set. The Small Form Factor committee (a temporary electronic industry group) attempted to create a standard, which became known as SMART. The initial standard described a communication protocol that ATA hosts could use to monitor and analyze, but it did not specify any metrics or analysis methods.
Many third-party applications can report SMART data. Unfortunately, due to differences between SSDs and HDDs, as well as interactions between the drive and computer, these applications may be inaccurate for some drives or systems.
As solid-state drives (SSDs) become more prevalent in data centers, personal computers, laptops, and any device or system requiring storage, it is important to consider factors beyond speed and capacity, especially when assessing SSD lifespan.
Two key metrics for explaining durability are: Total Bytes Written (TBW) and Drive Writes Per Day (DWPD). In this article, we explore the differences between them and how they are calculated.
Total Bytes Written (TBW)
In short, TBW refers to the total amount of data that can be written to an SSD over its entire lifespan. It is an excellent metric to indicate how long a drive can last under normal operating conditions. We calculate TBW by multiplying the drive capacity by the number of Program/Erase (P/E) cycles each NAND block can endure (as specified by the manufacturer), then dividing by the Write Amplification Factor (WAF).
The P/E cycle is determined by how many times a memory cell can be programmed and erased before becoming unreliable or inconsistent, while the WAF indicates the extra workload the SSD must perform when storing data.
NAND flash has inherent limits on the number of P/E cycles it can tolerate due to gradual degradation of the oxide layer that traps electrons within the memory cells with repeated use. Providing durability ratings for SSDs enables consumers to make informed decisions.
To illustrate TBW in real life:
If a 1.92TB SSD has a TBW rating of 3504, this means the drive can endure writing 3504TB of data before potential failure.
Drive Writes Per Day (DWPD)
On the other hand, DWPD offers a slightly different perspective by calculating how many times the drive can be fully written each day over the warranty period. This metric is especially important for high-intensity workloads such as servers or data centers.
We derive this ratio by comparing the TBW value to the product of warranty days multiplied by the total capacity. The formula used is:
DWPD = SSD TBW × 1000 / (365 days × warranty years × SSD capacity (GB))
For example, if a 7.68TB SSD has a TBW of 14016 and a warranty period of 5 years, the DWPD calculation is:
DWPD = 14016 × 1000 / (365 days × 5 years × 7680 GB)
This yields a result of 1 DWPD, indicating the SSD can handle a full drive write every day during the 5-year warranty period.
Conclusion
In summary, TBW is useful for understanding overall drive durability over its lifespan, while DWPD provides insight into the drive’s endurance under daily workloads—especially critical in enterprise and data center environments. Both metrics are key considerations when selecting an SSD, particularly for data-intensive tasks and continuous write operations.
S.M.A.R.T. stands for Self-Monitoring, Analysis, and Reporting Technology, which is part of the ATA standard. SMART data can be used to assess the "health status" of solid-state drives (SSDs). When enabled, it can warn users (administrators, software programs, etc.) of impending SSD failures.