QLC SSD (Quad Level Cell, Solid State Drive) is the new addition to the SSD (Solid State Drive) family after SLC, MLC, and TLC. But is it worth buying over the previous generations of SSD?
If you want a short and straight answer, Yes.
Yes, QLC SSD is totally worth buying if you buy at least 1 TB (Tera-Byte) of SSD because it has 140 GB of SLC Cache.
Let’s explore the difference in QLC SSD from other types.
How QLC is Different?
There are four types of SSD right now in the market. I am just going to explain basic differences in a table among them instead of talking gibberish.
SLC (Single-Level Cell) SSD contains only one bit (8 bits=1 Byte) per cell.
MLC (Multi-Level Cell) SSD contains two bits per cell.
TLC (Triple-Level Cell) SSD contains three bits per cell.
QLC (Quad-Level Cell) SSD contains four bits per cell.
So QLC SSD has the highest number of bits and thus more data in one cell which sounds promising but not really.
The more the number of bits that are stored in the cell, the more the cell has to work. QLC has 4 bits which mean 2^4=16 voltage levels. It is a real challenge to modify and write 16 voltage level at the nanometer level. Although QLC SSD does pack four times the data of SLC SSD. A single die of QLC Flash can store up to 125GB or 1 Tb of storage and Vendors can fit 16 dies in one SSD.
On the other hand, the durability is not reduced by four folds but at least 100 times that of an SLC SSD.
| TYPE OF SSD | DURABILITY Read/Write Cycles | BITS in a CELL | Read Time mili-sec | DOLLARS/GB | POWER Watts | |
| SLC | 100,000 P/E Cycles | 1 -bit (2 states) | 25 | 0.42 | 3 | |
| MLC | 10000 P/E Cycles | 2 -bit (4 states) | 50 | 0.35 | 5 | |
| TLC | 1000-1200 P/E Cycles | 3 -bit (8 states) | 75 | 0.15 | 1 | |
| QLC | 1000 P/E cycles | 4 -bit (16 states) | 100 | 0.10 | 0.2 |
In short, we are compromising on endurance and latency for price and low power.
QLC Flash is really Slow:
I am going to be honest here. The QLC Flash is really slow, like slower than a Hard Disk. The thing that makes it so fast is the huge chunk of SLC Cache attached to it. When this cache gets full, the real speed of QLC SSD starts to surface and it is just around 80 MBPS which is a lot slower than a hard disk drive.
Lets now talk about that SLC Cache which is the whole reason why anyone would buy a QLC SSD.
A 512GB QLC SSD has 76GB of the cache.
A 1 TB QLC SSD has 140GB of the cache.
A 2TB QLC SSD has 280GB of the cache.
It is worth mentioning here, we recommend you buy at least 1TB of QLC SSD because 140GB cache is enough for most uses.
Suppose you have a 1TB QLC SSD which has a cache of 140GB. This cache would not remain 140GB as you fill-up the drive, it will decrease. Look at the table below to see the relation between filling the SSD and its impact on SSD Cache.
So the cache memory has decreased to 76 GB at 50% filling of the 1 TB SSD which is still plenty for daily usage. But at more than 75% usage of the 1 TB SSD, the cache is only 12 GB which is like less than a game these days.
QLC SSD Capacity:
Looking at the graph for the cache, it would be fair to say to buy at least the 1 TB version of QLC SSD if want to enjoy the performance of an SSD and not a Hard disk.
It does not stop here. The lower storage variants also downgrades other specs.
| Item | Intel 660p 512GB | Intel 660p 1TB | Intel 660p 2TB |
| Sequential Read | 1500 MB/s | 1800 MB/s | 1800 MB/s |
| Sequential Write | 1000 MB/s | 1800 MB/s | 1800 MB/s |
| Random Read | 90000 IOPS | 150000 IOPS | 220000 IOPS |
| Random Write | 220000 IOPS | 220000 IOPS | 220000 IOPS |
| Cache | 76GB | 140GB | 280GB |
| Endurance | 100 TBW | 200 TBW | 400 TBW |
It is apparent that buying at least 1 TB of storage of QLC SSD is the smart thing to do. The 512GB SSD read, write are slow and its endurance 100 TBW (Terabytes written) is also really low.
QLC SSD Performance:
The important things you need to know to get the best performance out of your QLC SSD’s are:
- Buy 1 TB QLC SSD or higher capacities.
- Try to keep the drive filled less than 75% of its full capacity. At 75%, the SSD cache hits the lowest 12GB for 1TB SSD.
- Get the NVME SSD instead of SATA. The speed difference is at least 3 times.
If you do all of this and you are still not getting the performance, make sure your motherboards supports the full bandwidth of the SSD. So if you plan on changing components of your PC.
Give this a read:
Build A PC On Budget
Let’s now talk about how this new SSD technology performs in the synthetic benchmarks and in real-world usage.
The performance of a QLC SSD is generally on par with a TLC SSD. Though the performance of a QLC SSD really depends on how much it is filled. If you have filled you QLC SSD more than 50% of its capacity, the performance would drop exponentially. So for the tests below the QLC SSD is filled less than 50%.
Synthetic Benchmarks:
The benchmark was done on Crystal Mark.
To check IOPS (input output operations per second) AS SSD benchmark is used.
Game Loading Time:
This test was performed on intel 660p 1 TB SSD.
| Game Name | Loading Time |
| GTA 5 | 31 sec |
| Rise of Tomb Raider | 8 sec |
| The Witcher 3 | 14 sec |
Real World Usage:
In real world, we use windows loading time and copy, paste files to check the speed of SSD.
| SSD | Windows Boot TIme |
| Intel 600p | 9 seconds |
Now lets check the copy and paste speed of intel 600p.
So this is the problem with QLC SSD. As soon as the cache is full, the transfer speeds drops to even less than that of a Hard Disk (130 MBPS).
Endurance:
There is a big concern about the endurance of these QLC SSD’s. Let me show you how long a 1 TB QLC SSD will last. intel 660p 1 TB is rated for 200 TBW (Terabytes written).
So to calculate its life [(200x1024GB)/(5×365)]=112.2×0.93 (remove 7% overprovisioned space) = 104.36 GB/day for five years.
According to this calculation, you have to read/write 104.36 GB every day for five years to wear it out. Is that really possible? So I think this SSD will last for at least 8-9 years approximately. So do not miss out on this SSD because of the endurance.
The Problems With QLC SSD
QLD SSD is really cheap like 93$ right for 1 TB intel 660p. There are some things to know before you go on and buy a QLC.
- QLC SSD relies solely on the SLC cache in it. So if the cache runs out while you are transferring a big file, the performance degrades exponentially.
- The performance of QLC is great for up to 50% of the capacity.
- QLC is not as durable as other types of SSD. For 1 TB, it allows 200 TBW (Terabytes written) in contrast to TLC which is normally around 400 TBW (Terabytes written).
- Lower storage options like 256 or 512GB are not viable because of the low SLC Cache that comes with it.
Why Is QLC still worth it?
The whole article seemed like a rant about QLC SSD, but it’s not. Putting all the negatives of the QLC SSD above of positive works better as everyone should know what are they getting.
But now it is time for strong points of QLC SSD. We are going to look at 1 TB or above QLC SSD’s.
- QLC SSD gives an impression on the synthetic benchmarks like they are inferior to other SSD types. But the reality is, you would not feel any difference in the real-world performance of these QLC SSD’s. Be it gaming, running Adobe Photoshop, Adobe Premiere, running a SQL server or just casual use. It is good for just about anything.
- While it looks like the cache of the QLC SSD is limited and it will run out while you are doing some important task, it would not. The truth is our everyday tasks on a computer are limited to at most 100GB/s transfers. So this is why 140GB cache of 1TB SSD would be enough for 90% of the users.
- The Power consumption of QLC SSD’s is unheard of. They consume about 0.2 watts of power.
- Even if you think QLC is just not good. Still, it is a lot faster than a Hard drive. Even when the Cache is maxed out, the random read-write is still a lot better than any Hard Disk Drive. It is only a 30 dollars expensive than the 1 TB hard disk.
- Cheaper costs 0.10$/GB makes it a compelling solution to replace to mechanical Hard Disks.
- Higher storage (2TB) options have better transfer speeds of about 150MBPS equivalent to that of a Hard disk drive when the Cache is full.
Recommendations:
In the end, despite of all the points we raised in the article. We can say without any hesitation that QLC SSD’s are worth buying for the price they are being offered at.
Here are few tips to get the best QLC SSD and optimize its use:
- Buy at least a 1 TB QLC SSD, not lower. The 512 GB version has lower transfer rates, low IOPS, less SLC Cache than 1 TB version or higher.
- Fill your QLC SSD only up to 50% for the best performance and a maximum of 75% if you need it.
- Buy the NVME (Non-Volatile Memory Express) QLC SSD instead of SATA. As the NVME version has three times the read/write speeds of SATA.
- Buy the SSD version which is providing 5 years of warranty instead of 3 years warranty. Intel usually provides a 5 year warranty.
