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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  • Oxford Guy - Tuesday, August 7, 2018 - link

    No matter how terrible QLC is it is going to succeed in the market because consumers respond well to big and cheap.

    So, I think one interesting question is going to be how much disguising there will be of products having QLC. Microcenter, for instance, is apparently selling a TLC Inland drive, calling it MLC.
    Reply
  • piroroadkill - Wednesday, August 8, 2018 - link

    That's how I want QLC drives to be compared - to the best hard drives people might actually buy today to store their games on, for example.
    I'd love a cheap and large 4TB drive for my games, but it has to be both much faster than the HDD setup I use for games (2× 2TB 3.5" Seagate Hybrid drives in RAID0) and not too far off the same price.
    Reply
  • zodiacfml - Wednesday, August 8, 2018 - link

    Impressive performance. Easily beats my SATA 850 EVO in performance and twice the capacity I bought last December for the same price.
    There should be no reason for notebook manufacturers to settle for HDD except the cheapest laptops.
    Reply
  • mapesdhs - Wednesday, August 8, 2018 - link

    Given the 850 EVO's strong reliability reputation though, I wouldn't be overly eager to recommend this new QLC model for anyone wanting a decent degree of confidence that their data is safe. But then, most consumers don't have backup strategies anyway. :D Reply
  • Spunjji - Wednesday, August 8, 2018 - link

    If you want safe data, make regular backups. Anything else is a false sense of security! Reply
  • zodiacfml - Wednesday, August 8, 2018 - link

    I think the limiting factor for reliability is the electronics/controller, not the NAND. You just lose drive space with a QLC much sooner with plenty of writes. Reply
  • romrunning - Wednesday, August 8, 2018 - link

    Given that you can buy 1TB 2.5" HDD for $40-60 (maybe less for volume purchases), and even this QLC drive is still $0.20/GB, I think it's still going to be quite a while before notebook mfgs replace their "big" HDD with a QLC drive. After all, the first thing the consumer sees is "it's got lots of storage!" Reply
  • evilpaul666 - Wednesday, August 8, 2018 - link

    Does the 660p series of drives work with the Intel CAS (Cache Acceleration Software)? I've used the trial version and it works about as well as Optane does for speeding up a mechanical HDD while being quite a lot larger. Reply
  • eddieobscurant - Wednesday, August 8, 2018 - link

    Wow,this got a recommended award and the adata 8200 didn't. Another pro-intel marketing from anandtech. Waiting for biased threadripper 2 review. Reply
  • BurntMyBacon - Wednesday, August 8, 2018 - link

    The performance of this SSD is quite bipolar. I'm not sure I'd be as generous with the award. Though, I think the decision to give out an award had more to do with the price of the drive and the probable performance for typical consumer workloads than some "pro-intel marketing" bias. Reply

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