The most important part of SSD is the flash memory particle which is responsible for storing data, which largely determines the performance and service life of SSD. "Buy SSD, seven points is in the purchase of flash memory," the statement is enough to show its importance. Flash memory was originally born in a silicon wafer. According to the test results, flash chip manufacturers cut and select qualified chips, and then package them. As a result, it has become a familiar and commonly known flash memory. Since its birth, flash memory particles have experienced four types: SLC, MLC, TLC and QLC. According to the time sequence, SLC is the oldest and QLC is the youngest. They coexist for a long time, but their application fields are quite different. The reason is closely related to their own characteristics.
In SLC flash memory, a storage unit can only store 1 bit of data, that is, a 0 or a 1, so a storage unit has only two states.
In MLC flash memory, a storage unit can be packed with 2 bits of data, 0 and 1 can be arranged and combined, with four states of 10, 11, 00 and 01. By analogy, to the latest generation of QLC flash memory, a storage cell has 16 storage states, and the storage capacity is 8 times of SLC flash memory.
However, God opened one door and closed another for SSD. Although the updating of flash memory type brought about a substantial increase in capacity, it was at the expense of speed and life.
Unlike mechanical hard disk, SSD flash memory can erase and write a limited number of times, and this number is the life of flash memory. When the flash memory number of erasure reaches the limit, the flash memory will be damaged and the stored data will be lost. SLC flash memory has 100000 erase times, and to the latest generation of QLC flash memory, only about 1000 times. Under the same capacity and service conditions, the theoretical life of the two is 100 times different.
With the development of flash technology, it can be said that with the development of new generation of flash memory. But this is actually the active choice of the market. SSD has only begun to popularize the consumer market in recent years. In the long process of evolution, nothing hinders the popularity of SSD is the price. SSD is the key to reduce the cost of SSD. Today, it is gratifying to see that compared with SSD equipped with SLC flash memory, the price of SSD with TLC flash memory has dropped to affordable level. At the same time, even if the life is discounted, today's SSD can still meet the needs of ordinary people, so it is not a problem to use it for 3-5 years easily.
Therefore, the main problem of SSD today is not life, but the sudden decrease of speed when its capacity is about to be filled. The cause of this problem is related to the erase process of flash memory. It is different from that when the old data is written to the SSD directly, it can not be covered by the new data. When there is new data to write, if the space capacity is not enough, SSD needs to recycle the old data, erase and then write. This process has been written to enlarge (for related introduction of write amplification, you can click on the MEMO column of GALAXY official account menu bar for viewing).
Write amplification means more complex steps, longer time consuming and more writes. Therefore, if the SSD is too full, whether it is running speed or time life, will be affected, varying degrees of decline.
How to avoid SSD performance degradation caused by excessive data storage?
For entry-level SSDs, the available capacity is usually reduced, and a part of space is reserved to avoid full SSD. This is why many SSDs on the market have a capacity of 240g or 480g instead of 256g and 512g. Medium and high-end SSDs will be equipped with additional cache to reduce write amplification. For example, Yingchi hofpro m.21tb provides a large cache of up to 1GB.
Of course, the above methods are mainly used by SSD manufacturers. For users, they should form good habits in daily use. For infrequent files, they should be cleaned up in time to ensure that SSD has enough space to meet their daily reading and writing requirements.