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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  • jjj - Tuesday, August 7, 2018 - link

    Not bad, at least for now when there are no QLC competitors.
    The pressure QLC will put on HDDs is gonna be interesting too.
  • npz - Tuesday, August 7, 2018 - link

    Well at least the price is reflected in the performance, with the MX500 beating the 660p when both are full. As far as scenarios where you'd go from SLC to QLC I would be much more cautious about generalizing too much. A lot of people use SSDs as scratch drives for their work (DAW, video editing, recording, etc) and it seems more than likely to hit it in those usage scenarios Reply
  • StrangerGuy - Tuesday, August 7, 2018 - link

    "A lot of people use SSDs as scratch drives for their work (DAW, video editing, recording, etc)"

    A lot of people relative to the entire market? No.
    Is this drive intended for power users/professionals? No.
    Is QLC bringing a lot more GB/$ at MSRP prices for 90%+ of the market? Yes.
    Is the worst case performance even remotely applicable to its intended market? No
    So did you just say a dumb comment while disguised a concern troll? Yes.
  • npz - Wednesday, August 8, 2018 - link

    A lot people who would bother purusing sites like Anandtech yes. The people who would run more comprehensive benchmarks, as opposed to just buying a cheap SSD is the lot of people in the alot of.. I refer to. Of course you just disregarded the rest of my statement acknowleding the fact that it's cheap didn't you? Just so you could go on with your smart ass here. Reply
  • npz - Wednesday, August 8, 2018 - link

    And I specifically refer to "worst case" because I argue it is NOT worst case, but it becomes a rather typical case for certain use--going out of SLC to QLC, which would NOT be seen by just quick benchmarks like a lot of people cite on Amazon reviews via Crystaldisk benchmarks. Reply
  • Valantar - Wednesday, August 8, 2018 - link

    a) If you're enough of a power user to need a scratch disk and use it heavily enough to fill its SLC cache, you really ought to be buying proper equipment and not low-end drives.
    b) if you're -"- you really ought to educate yourself about your needs, or employ someone with this knowledge
    c) If you're not -"-, stop worrying and enjoy the cheap SSDs.

    Tl;dr: workstation parts for workstation use; cheapo parts for basic use.
  • damianrobertjones - Tuesday, August 7, 2018 - link

    These drives will fill the bottom end... allowing the mid and high tiers to increase in price. Usual. Reply
  • Valantar - Wednesday, August 8, 2018 - link

    Only if the performance difference is large enough to make them worth it - which it isn't, at least in this case. While the advent of TLC did push MLC prices up (mainly due to reduced production and sales volume), it seems unlikely for the same to happen here, as these drives aim for a market segment that has so far been largely unoccupied. (It's also worth mentioning here that silicon prices have been rising for quite a while, and also affects this.) There are a few TLC drives in the same segment, but those are also quite bad. This, on the other hand, competes with faster drives unless you fill it or the SLC cache. In other words, higher-end drives will have to either aim for customers with heavier workloads (which might imply higher prices, but would also mean optimizations for non-consumer usage scenarios) or push prices lower to compete. Reply
  • romrunning - Wednesday, August 8, 2018 - link

    Well, QLC will slowly push out TLC, which was already pushing out MLC. It's not just pushing the prices of MLC/TLC up, mfgs are slowing phasing those lines out entirely. So even if I want a specific type, I may not be able to purchase it in consumerspace (maybe enterprise, with the resultant price hit).

    I hate that we're getting lower-performing items for the cheaper price - I'd rather get higher-performing at cheaper prices! :)
  • rpg1966 - Tuesday, August 7, 2018 - link

    "In the past year, the deployment of 64-layer 3D NAND flash has allowed almost all of the SSD industry to adopt three bit per cell TLC flash"

    What does this mean? n-layer NAND isn't a requirement for TLC is it?

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