SSDs based on NAND flash memory are becoming more and more accepted as one of the necessary accessories for installation. HDD mechanical disks are increasingly unfettered, if not for the past two years, memory chips have experienced a two-year price increase. In 2018, 480-512GB of SSDs should be available in the market, and people's demand for SSD capacity is also increasing. QTL flash memory has also appeared since TLC dominated the SSD market.
In July of last year, Toshiba announced the QLC flash memory, with a core capacity of 768Gb, and created a new record for NAND capacity. At the end of May this year, Micron announced Intel’s own QLC flash memory and introduced the new 5210 ION series hard drive, officially commercialized. QLC flash technology, but its arrival has made many people full of suspicions, many readers are questioning the performance and reliability of QLC flash memory, and even think this is a retrogression. So what exactly is the truth?
Before understanding the QLC flash memory, we first briefly introduce the differences and advantages and disadvantages of different types of NAND flash memory.
The basic principle of NAND flash memory: QLC capacity, but the performance has also deteriorated
NAND flash memory is based on how many bits of information the memory cells can then apply to different voltages to realize information storage. Many people know that NAND flash memory has SLC, MLC, and TLC points. Now that there are more QLC flash memories, how much difference is there between them? What?
SLC: Full name Single-Level Cell, each Cell unit stores 1 bit information, that is, only 0, 1 two kinds of voltage changes, the structure is simple, the voltage control is also fast, reflecting the characteristics of long life, strong performance, P/E life at 1 Between 10,000 and 100,000 times, the disadvantage is that the capacity is low and the cost is high. After all, a Cell unit can store only 1 bit of information.
MLC: The full name is Multi-Level Cell, it is actually corresponding to SLC, NAND flash memory other than SLC is MLC type, and we often say that MLC refers to 2bit MLC.
Each cell stores 2 bits of information. There are four variations of voltages 000, 01, 10, and 11. Therefore, it requires more complex voltage control than SLC, and the pressurization process takes longer. This means that the write performance is reduced. Reliability has also declined, P/E life varies from 3000 to 5000 times depending on the process, and some are even lower.
TLC: That is Trinary-Level Cell, exactly 3bit MLC Each cell stores 3 bits of information. There are 8 changes in voltage from 000 to 111. The capacity is increased by 1/3 again compared to MLC. The cost is lower, but the architecture is more complicated, the P/E programming time is longer, and the writing speed is slower. The lifetime of /E is also reduced to 1000-3000 times, and part of the situation will be lower.
The QLC now listed is the Quad-Level Cell, or 4bit MLC There are 16 changes in the voltage from 0000 to 1111, and the capacity has increased by 33%. However, the write performance will reduce the P/E life again.
How can we understand these technological changes? We can give a simple example. Think of NAND flash memory as a university dormitory. SLC flash memory is equivalent to a doctoral dormitory, often a single room, so the cost is high, but doctors can do better work, and MLC Flash memory is a master's dormitory, with two people in one room, the cost is reduced a lot, but the master's research is naturally better than doctoral.
The TLC is a three-person university dormitory. The QLC is a four-person dormitory. It may be a non-popular professional school slag. The fighting power is much worse than the previous three, but it is also a college student.
Compared with the performance of QLC flash memory and TLC flash memory, the write performance is further reduced
Specific to the performance, Micron has done a detailed interpretation, the first read speed is not much worse than TLC flash memory, both in the SATA interface can reach 540MB/s speed, QLC flash memory is mainly poor in the writing speed, because it is born P /E programming time is longer than MLC, TLC, slower, continuous write speed is reduced from 520MB/s to 360MB/s, random performance is reduced from 9500 IOPS to 5000 IOPS, the loss is nearly half.
At the same time, MTTF's time between failures has dropped from 3 million hours to 2 million hours. Performance and reliability have not gone down.
23D stack technology blessing, QLC flash encountered a good time 3D stack technology blessing, QLC flash encountered a good time
Just as the TLC flash memory was tested when it first came out, performance and reliability degradation are the inevitable shortcomings of QLC flash memory. Should we be worried about QLC flash memory or reject QLC flash memory?
Intuitively, this should be the case, but we also need to understand that NAND flash memory is now entering the 3D NAND era. Unlike the era of 2D NAND, the QLC flash memory in the 3D NAND era is also different from the QLC flash memory in the 2D NAND era. This is decided by both parties' technology routes.
In the era of 2D NAND flash memory, manufacturers have to constantly improve NAND process technology in order to pursue NAND capacity enhancement. Therefore, NAND has entered the 30nm, 20nm, and 10nm eras from 50nm in previous years.
This is like the continuous upgrading of the processor technology. The advantage is that the transistor density is increased, the NAND capacity is increased, and the cost is reduced. However, the increase in the NAND process also means that the silicon dioxide layer for blocking electrons becomes thinner and thinner, resulting in reliability. When the MLC, TLC, and QLC flashes move through the silicon dioxide layer step by step, the oxide layer becomes thin, which is why the P/E lifetime decreases.
However, in the 3D NAND era, upgrading NAND capacity is not relying on the microfabrication process, but on the number of layers in the stack, so the process becomes unimportant. NAND manufacturers can even use previous processes, such as Samsung's initial 3D NAND flash memory. Or 40nm process, reliability is much higher than the 20nm, 10nm level process.
Because of this, QLC flash has won a different treatment from TLC. TLC flash memory was still available in the era of 2D NAND flash memory, so it suffered a lot of life, performance test, the initial release of TLC flash P/E life is only 100-150 Times, can not see, but Micron, Intel's QLC flash memory directly using 3D NAND technology, P/E life expectancy reached 1000 times, completely without losing the current 3D TLC flash memory.
You may not have noticed that this initial launch of the 5210 ION HDD is for the enterprise market, not for the consumer market. The former has higher reliability requirements than the consumer market. Intel and Micron do this for QLC flash memory. Life, reliability and confidence.
In addition, the P/E lifetime is not constant. With advances in NAND technology and improved error correction techniques, P/E life expectancy will increase. TLC flash memory has gradually increased from less than 500 to 1,000 or more. High level, reliability has been verified, QLC will also be the same.
Storage needs have changed, and the era of ultra-capacity SSD is approaching
The emergence of QLC flash memory has the need for NAND manufacturers to continuously reduce costs. However, the fundamental problem is that the market demand is changing. We generally think that the storage requirements are memory, SSD and HDD, and the performance is gradually reduced, and the capacity is gradually upgraded. Raise.
But now there is an additional SCM (system-level storage) between memory and SSD. This is what NVDIMM memory Intel released a few days ago. Its performance is lower than that of DDR4, but it is higher than that of SSD, and at the same time it does not lose data. .
There will also be an extra tier between SSD and HDD. That is the large-capacity SSD. Terabytes are all at the starting level. It is also a piece of cake to reach 10TB in the future. However, the performance of this super-capacity SSD is better than that of existing MLC, TLC flash memory. Hard disk, its goal is HDD hard disk.
That's right, once the QLC flash memory is mass-produced, the write speed of the SSD hard disk used by it may be about 200-300MB/s, but the 5000+ random write performance is still much higher than the HDD hard disk, and the capacity can reach 10 -100TB level.
Toshiba previously described this in the QLC flash memory. The performance of the 100TB QLC flash SSD is similar to that of an array of 12 8TB HDD hard drives, all of which are 3000MB/s, but the random performance of 50K IOPS is much better than that of HDD arrays. At the same time, the standby power consumption of 0.1W is much lower than that of the 96W of the HDD array. This is also the reason why Micron first released QLC flash memory in the enterprise market. In this part of the demand, the QLC hard disk drive is the HDD HDD.
Before Micron predicted 2021, the average SSD capacity could reach 597GB, which sounds not high, but they also predict that each PC user will use 4 SSDs on average. This is not to say that we buy 4 SSDs with 600GB capacity. It may be such a combination - 480/512GB MLC or QLC hard disk as the main disk, installation system and commonly used software.
At the same time, there will be 2TB or even 4TB QLC flash SSDs as warehouse disks to save movies or games. In this case, the read speed is high, the write speed is very low, and the advantages of QLC hard disks can be perfectly used to avoid poor write performance. Shortcomings.
to sum up:
The era of QLC flash memory has come. In addition to Micron, Intel's first QLC hard drive, Toshiba, Western Digital's QLC flash memory has also begun a small amount of shipments, Samsung, SK Hynix's QLC flash memory is also on the road, but there is no high-profile public only.
It is normal for everyone to worry about QLC flash memory. After all, QLC flash memory is in principle worse than MLC or even TLC. However, QLC flash memory in the 3D NAND era is totally different from TLC and QLC in the 2D NAND era. The P/E lifetime is not a problem, and it is not worse than the TLC flash memory.
The biggest temptation of QLC flash memory is that it will have more capacity in the future. The popularization of 10TB capacity in the desktop market depends on it. The enterprise-class market will even achieve 100TB capacity without losing HDD hard drives. At the same time, the continuous performance of the QLC hard disk is even better than random performance. HDD hard drives, power consumption, noise, etc. are also not comparable, and are really alternatives to HDD hard drives.
