Conclusion

As the first SSD with QLC NAND to hit our testbed, the Intel SSD 660p provides much-awaited hard facts to settle the rumors and worries surrounding QLC NAND. With only a short time to review the drive we haven't had time to do much about measuring the write endurance, but our 1TB sample has been subjected to 8TB of writes and counting (out of a rated 200TB endurance) without reporting any errors and the SMART status indicates about 1% of the endurance has been used, so things are looking fine thus far.

On the performance side of things, we have confirmed that QLC NAND is slower than TLC, but the difference is not as drastic as many early predictions about QLC NAND suggested. If we didn't already know what NAND the 660p uses under the hood, Intel could pass it off as being an unusually slow TLC SSD. Even the worst-case performance isn't any worse than what we've seen with some older, smaller TLC SSDs with NAND that is much slower than the current 64-layer stuff.

The performance of the SLC cache on the Intel SSD 660p is excellent, rivaling the high-end 8-channel controllers from Silicon Motion. When the 660p isn't very full and the SLC cache is still quite large, it provides significant boosts to write performance. Read performance is usually very competitive with other low-end NVMe SSDs and well out of reach of SATA SSDs. The only exception seems to be that the 660p is not very good at suspending write operations in favor of completing a quicker read operation, so during mixed workloads or when the drive is still working on background processing to flush the SLC cache the read latency can be significantly elevated.

Even though our synthetic tests are designed to give drives a reasonable amount of idle time to flush their SLC write caches, the 660p keeps most of the data as SLC until the capacity of QLC becomes necessary. This means that when the SLC cache does eventually fill up, there's a large backlog of work to be done migrating data in to QLC blocks. We haven't yet quantified how quickly the 660p can fold the data from the SLC cache into QLC during idle times, but it clearly isn't enough to keep pace with our current test configurations. It also appears that most or all of the tests that were run after filling the drive up to 100% did not give the 660p enough idle time after the fill operation to complete its background cleanup work, so even some of the read performance measurements for the full-drive test runs suffer the consequences of filling up the SLC write cache.

In the real world, it is very rare for a consumer drive to need to accept tens or hundreds of GB of writes without interruption. Even the installation of a very large video game can mostly fit within the SLC cache of the 1TB 660p when the drive is not too full, and the steady-state write performance is pretty close to the highest rate data can be streamed into a computer over gigabit Ethernet. When copying huge amounts of data off of another SSD or sufficiently fast hard drive(s) it is possible to approach the worst-case performance our benchmarks have revealed, but those kind of jobs already last long enough that the user will take a coffee break while waiting.

Given the above caveats and the rarity with which they matter, the 660p's performance seems great for the majority of consumers who have light storage workloads. The 660p usually offers substantially better performance than SATA drives for very little extra cost and with only a small sacrifice in power efficiency. The 660p proves that QLC NAND is a viable option for general-purpose storage, and most users don't need to know or care that the drive is using QLC NAND instead of TLC NAND. The 660p still carries a bit of a price premium over what we would expect a SATA QLC SSD to cost, so it isn't the cheapest consumer SSD on the market, but it has effectively closed the price gap between mainstream SATA and entry-level NVMe drives.

Power users may not be satisfied with the limitations of the Intel SSD 660p, but for more typical users it offers a nice step up from the performance of SATA SSDs with a minimal price premium, making it an easy recommendation.

Power Management
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  • eastcoast_pete - Tuesday, August 7, 2018 - link

    Firstly, thanks for calling me one of the "idiots salivating over elusive real world endurance rating numbers". I guess it takes one to know one, or think you found one. Second, I am quite aware of the need to have a sufficient sample size to make any inference to the real world. And third, I asked the question because this is new NAND tech (QLC), and I believe it doesn't hurt to put the test sample that the manufacturer sends through its paces for a while, because if that shows any sign of performance deterioration after a week or so of intense use, it doesn't bode well for the maturity of the tech and/or the in-house QC.
    And, your last comment about your 80 GB near first gen drive shows your own ignorance. Most/maybe all of those early SSDs were SLC NAND, and came with large overprovisioning, and yes, they are very hard to kill. This new QLC technology is, well, new, so yes I would like to see some stress testing done, just to see if the assumption that it's all just fine holds, at least for the drive the manufacturer provided.
    Reply
  • Oxford Guy - Tuesday, August 7, 2018 - link

    If a product ships with a defect that is shared by all of its kind then only one unit is needed to expose it. Reply
  • mapesdhs - Wednesday, August 8, 2018 - link

    Proof by negation, good point. :) Reply
  • Spunjji - Wednesday, August 8, 2018 - link

    That's a big if, though. If say 80% of them do and Anandtech gets the one that doesn't, then...

    2nd gen OCZ Sandforce drives were well reviewed when they first came out.
    Reply
  • Oxford Guy - Friday, August 10, 2018 - link

    "2nd gen OCZ Sandforce drives were well reviewed when they first came out."

    That's because OCZ pulled a bait and switch, switching from 32-bit NAND, which the controller was designed for, to 64-bit NAND. The 240 GB model with 64-bit NAND, in particular, had terrible bricking problems.

    Beyond that, there should have been pressure on Sandforce's decision to brick SSDs "to protect their firmware IP" rather than putting users' data first. Even prior to the severe reliability problems being exposed, that should have been looked at. But, there is generally so much passivity and deference in the tech press.
    Reply
  • Oxford Guy - Friday, August 10, 2018 - link

    This example shows why it's important for the tech press to not merely evaluate the stuff they're given but go out and get products later, after the initial review cycle. It's very interesting to see the stealth downgrades that happen.

    The Lenovo S-10 netbook was praised by reviewers for having a matte screen. The matte screen, though, was replaced by a cheaper-to-make glossy later. Did Lenovo call the machine with a glossy screen the S-11? Nope!

    Sapphire, I just discovered, got lots of reviewer hype for its vapor chamber Vega cooler, only to replace the models with those. The difference? The ones with the vapor chamber are, so conveniently, "limited edition". Yet, people have found that the messaging about the difference has been far from clear, not just on Sapphire's website but also on some review sites. It's very convenient to pull this kind of bait and switch. Send reviewers a better product then sell customers something that seems exactly the same but which is clearly inferior.
    Reply
  • southleft - Tuesday, May 14, 2019 - link

    SSDs replaced under warranty by the maker can sometimes have a silver lining, so to speak. Some years ago we had an Intel X25 80GB fail. Intel replaced it with a newer model 320 which was basically the same but updated to SATA III. We also had a Sandisk Ultra 120GB fail, and Sandisk replaced it with an Ultra 2. These newer replacement models are still running OK some 6 years later, for what it's worth! Reply
  • chrcoluk - Wednesday, September 25, 2019 - link

    I agree, this is more important than hitting embargo date for publishing.

    Its the content not the date that matters. If it takes a year to do it, then so be it. I never buy hardware on release date, to me that's just stupid.
    Reply
  • Oxford Guy - Tuesday, August 7, 2018 - link

    People trusted Samsung with the 840 and then, oops...

    The real rule is verify then trust.
    Reply
  • mapesdhs - Wednesday, August 8, 2018 - link

    One thing about the 840 EVO issue which was a real pain was trying to find out if the same thing affected the standard 840. In the end my conclusion was yes, but few sites bothered to mention it. Oddly enough, of the many SSDs I have, one of the very few that did die was a standard 840. I never bought an 840 EVO because of the reports that came out, but I have a fair few 840 Pros and a heck of a lot of OCZs. Reply

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