How fast are different types of SSD storage (SLC, MLC, TLC, QLC)?

Question

I would like to buy an SSD which I regularly plan on writing large files (RAW video files). I am trying to decide between an QLC, TLC, and MLC SSD, but the prices increase in that order.

What are the speeds of SLC, MLC, TLC, and QLC NAND storages? This will help me decide what type of drive I want. I am thinking of going with the TLC storage, but if my file transfer speeds will throttle significantly I will consider going for the MLC storage, but I want to know first how much of an advantage this will bring me.

An example of what I mean: Samsung produces a few lines of SATA SSDs—the Pro, the Evo, and the Qvo. They use MLC, TLC, and QLC storage respectively. However, in each of their specifications it is listed that their read and write speeds are around ~550 MB/s. I am looking to understand the actual speed that I will experience after the buffer has been used up, which will undoubtedly be different for each type of SSD.

I also noticed that one of my SSDs throttles to about 20 MB/s when copying large files over. This seems extremely low to me, and I'm wondering if it is faulty or if the slower NAND storage is just that slow.

Answer 1

The speeds of a specific SSD will be listed by the manufacturer, but this is mainly affected by the overall design and interface that it uses. A SATA SSD for example will be slower than an m2 NVME pcie SSD.

The channel design with SLC, MLC, TLC, and QLC can instead affect the overall lifespan of sectors on the storage drive. Each cell in an SSD has a number of times that data can be written to it; think of it as an odometer. In these different channel designs, different numbers of bits can be stored in a cell. SLC can store one bit, MLC 2 bits, TLC 3 bits, QLC 4 bits. The more bits that can be written to a cell means that the cell takes more millage, and then it's lifespan is shorter.

The TBW rating of a drive can tell you how many terabytes can most likely be written to the device. Some brands like Samsung devices can communicate with a software to tell what the TBW is at any time, so like an odometer, you know how much of the lifespan you have used up.

The channel doesn't affect the speed so much, but the more bits in a cell can mean that it takes longer to write. But this isn't the biggest factor for the speed rating of a drive.