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QLC vs. TLC: Which is the Better SSD?

QLC vs. TLC: Which is the Better SSD?

Both quad-level cell (QLC) solid-state drives (SSDs) and triple-level cell (MLC) SSDs can provide excellent data storage solutions, but you will need to research which is the best for your particular needs. 

QLC SSDs excel in certain areas and come with certain disadvantages. The same goes for TLC SSDs. Another thing to consider is that TLC SSDs have been on the market a bit longer and there are certain advantages to products that have been out there and iterated on many times already, allowing manufacturers more time to iron out the bugs and produce the best product possible.

QLC vs. TLC — What’s the Difference?

The primary difference between QLC SSDs and TLC SSDs is the number of charge levels and the corresponding storage capability: QLC SSDs have 16 different charge levels, compared to TLC SSDs’ eight, which means QLC SSDs can store four bits of data per cell, compared to three bits of data per cell for TLC SSDs. 

TLC and QLC SSDs also differ in terms of:

Cost: Because of their bigger capacity, QLC SSDs can deliver per-terabyte costs that match or beat those of hard-disk drives (HDDs). Because cost per unit of storage decreases as storage capacity increases, a QLC SSD is almost always going to be cheaper than a TLC SSD.

Reliability: Because they have sixteen different voltage levels, compared to TLC’s eight, QLC SSDs are usually less reliable than TLC SSDs because the smaller difference between the voltage levels make the read process more sensitive to noise, leading to a higher bit error rate.  

Performance: QLC SSDs are generally slower than TLC SSDs because they have eight more voltage levels, each of which needs to be checked and translated back to bits when reading data. 

Endurance: The more charge levels an SSD has, the fewer P/E or write cycles it can support. Thus, QLC SSDs have lower write endurance than TLC SSDs.

Should I buy a QLC or TLC SSD for my NAS, SAN, or Server?

Now that we’ve covered the key differences between QLC SSDs and TLC SSDs, let’s take a closer look at the situations where you might use one over the other. 

While TLC drives have become mainstream and now hold the largest market share, QLC drives are starting to catch up. However, it is unlikely that their adoption will be as quick as that of TLC SSDs unless their performance improves significantly. 

QLC drives work great for their intended purpose—ie, as low-cost drives to replace HDDs in read-heavy workloads. Sometimes their peak performance can rival that of even high-end TLC-based drives, depending on the manufacturer, but their performance in steady-state situations still lags far behind. 

As mentioned above, QLC SSDs deliver a lower storage cost per capacity than TLC SSDs, so if your SAN or NAS has, or will have, more read than write operations, a QLC drive is probably the best choice. 

Incidentally, many of today’s most popular enterprise-grade applications are more read-heavy than write-heavy. 

These include:

  • Data analytics
  • AI
  • NoSQL databases
  • Streaming media and content delivery networks

So if your application is going to involve any of the above, it’s likely that you will benefit from choosing QLCs over TLCs.

When to Use TLC SSDs over QLC SSDs

If performance, endurance, and reliability are more important to you than cost or storage capacity, a TLC SSD is generally going to be a better choice than a QLC SSD, assuming your budget can accommodate the higher price of the TLC SSDs. 

The better performance and reliability of TLC SSDs typically make them a better choice for things like:

  • USB drives
  • Enterprise- and consumer-grade SSDs
  • Storage cards for digital cameras and mobile phones

The Verdict: QLC SSDs vs. TLC SSDs

QLC SSDs can store more data than TLC SSDs and they also cost less. However, they don’t perform as well or last as long, and they can be more error-prone. TLC SSDs perform better and last longer than QLC SSDs but store less data and cost more. 

It’s very important to keep in mind that the quality of SSDs can vary greatly from manufacturer to manufacturer, and also that your needs should drive your choices.

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