SSD Durability Ratings,

Typically SSD durability is expressed as terabytes written( TBW ) i.e.  the number of terabytes that can be written to a drive before it fails.  Typically a 500 GB model  has a TBW rating of 600; TBWs ratings are conservative estimates;

Flash memory loses reliability when the cells are too close together. Stacking  memory cells on top of each others increases capacity and reduces interference. This stacking is termed  3D NAND.

Wear Leveling:

SSD memory cells start degrade immediately from first use. To help keep drives in good shape for longer, manufacturers include wear technology, which uses an algorithm that writes data to memory cells as equally as possible. Instead of writing a certain block in one section of the drive all the time, it distributes data evenly, so all cells are filled at relatively the same rate.

Dynamic Wear Leveling

There are different types of wear leveling. Dynamic  wear leveling creates a map that links logical block addresses (LBAs) from the OS to the physical flash memory cells. Each time the OS writes new data, the  address map is updated and the original blocks are marked as invalid data. Every time a block of data is written to the flash memory it is written to a fresh location.

Static Wear Leveling

Static wear leveling works in a similar way as  Dynamic Wear Leveling but with DWL the  blocks that do not change are periodically moved and made available for use by other data. This moving around of cell  blocks means the  SSD will continue to operate and most cell blocks will have optimum usage.

Global Wear Leveling

DWL and SWL are implementd on a chip by chip basis. Ineffective blocks in physically different chips varies. A specific flash memory chip can have all its data blocks worn out while another one can have all the blocks still active.  Global Wear Leveling GWL  manages the blocks of data cells on the chips as a single pool and ensures  all the cells in all the chips wear consistently

Wear Levels Compared

The following table is a brief comparison concerning wear leveling:

Item	Static	Dynamic
Endurance	Longer life expectancy	Shorter life expectancy
Performance	Slower	Faster
Design complexity	More complex	Less complex
Typical use	Industrial-grade flash drives	Consumer-grade flash drives

Program Erase Cycle.

Program/Erase Cycle, the P/E Cycle translates to a drive’s endurance. When cell blocks write, erase, and rewrite data, an electrical charge damages the oxide layer of the cell’s floating gate transistor. Over time  P/E cycle affected blocks no longer hold a charge are are of no use.

SSD Choices. 

For those wishing to simply increase boot and load speeds for an improved browsing experience TLC drives are the best option. If you are constantly uploading, saving  and downloading new files for work purposes then MLC series are the best option.

SSD Usage.

Media files are large and take up a lot of space. If you’re constantly adding photos, videos etc  you’ll need the right capacity and high R/W speeds.  If you’re not running resource heavy applications, then you don’t need the fastest drive available.

SSD Cache.

SSD,s use cache in which data is briefly stored before it’s written to the drive. Cache is critical for boosting SSD performance. They’re typically comprised of SLC or MLC NAND. When the cache is full, performance tends to drop significantly—this is especially true for some TLC and most QLC drives.

SSD SATA III

SATA 111 is a common interface used  on SSD,s  and is how the drive connects to the motherboard. SATA III has a maximum throughput of 600 megabytes per second.

NVMe SSD,s 

This interface connects an SSD to the motherboard. NVMe travels over PCIe for blazing-fast speeds.  NVMe drives are circa  three times faster than SATA III.

Learn more about SSD Failures and Data Recovery.