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Western Digital introduced solid-state drives PC SN5000S based on QLC flash memory chips, which demonstrate higher performance in terms of reading and writing speed than its predecessors based on faster TLC memory.
PC SN5000S — the latest series of consumer solid-state drives with a volume of up to 2 TB, produced by the company in the full-size M.2 2280 format and the compact M.2 2230 format. The series replaced the SN740 PC drives, which are offered in the same capacities.
Western model Digital PC SN5000S with a volume of 2 TB with QLC memory, the write speed is up to 16,5%, and the read speed is up to 15,5% faster compared to the SN740 model of the same volume, but with TLC memory. The SN740 model with a volume of 1 TB is still slightly faster in writing than the SN5000S, but in reading speed it lags behind the novelty by 14,3%.
The advantage of the SN5000S drive with a volume of 2 TB over its predecessor is also 100 TBW (terabytes of overwritten information) more reserve of work resource. However, the resource of the new SSD with a volume of 1 TB is 100 TBW lower (300 TBW against 400 TBW in the SN740 of the same volume). The disadvantage of the new SSD series can be considered a slightly higher power consumption indicator.
As a rule, drives based on NAND QLC flash memory lag behind SSDs based on other types of flash memory. This is explained by the fact that the QLC memory stores four bits of information in one cell, which affects the final performance not for the better. Recall that SLC flash memory stores one bit of information per cell, MLC memory - two bits of information, and TLC - three bits. The fewer bits stored in a cell, the faster and more durable it is. While the ability to store more bits per cell increases memory density, the need to read and write more bits results in lower performance and generally increases wear and tear on NAND memory.
There are several ways to improve the performance of drives with QLC memory and other multi-bit NAND memory types. The use of SLC cache memory as part of the drive is probably obvious. Although QLC, as mentioned above, stores four bits of information in a cell, a drive with an SLC cache does not need to fill all four bits of information during recording. SSDs will perform much better if you mark some of the memory cells as pseudo-SLC. True, empty cells are used for this, which ultimately reduces the available volume of the SSD itself.
Despite the shortcomings of QLC memory and other multi-bit types of NAND flash memory, some manufacturers, for example, Samsung, are interested in the further development of this technology. Due to the fact that ordinary consumers do not always need better performance and reliability, and when choosing an SSD, preference is often given based on price and storage capacity, SSD models based on QLC memory are usually the most economical choice for the buyer. In turn, low-density SLC memory drives are better suited for servers, where high performance and reliability are much more useful.
