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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  • npz - Tuesday, August 7, 2018 - link

    IMO no, not from USB sticks. There's this whitepaper from Dell concerning retention for their enterprise SSDs:
    http://www.dell.com/downloads/global/products/pvau...

    It depends on the how much the flash has been used (P/E cycle used), type of flash, and
    storage temperature. In MLC and SLC, this can be as low as 3 months and best case can be more than 10 years. The retention is highly dependent on temperature and workload.

    The pattern that I've noticed is that the more write durability and write-performance-oriented, the lower the retention rate (so it's actually inversely related)

    Now JEDEC specifies 1 year retention but who knows how many SSDs really follow it. As we saw with Samsun 840 it wouldn't have lasted a year without the firmware update, but that still requires periodically powered on. I still don't think it would last a full year after being tortured, then unplugged.
    Reply
  • Oxford Guy - Tuesday, August 7, 2018 - link

    And yet every article about it said Samsung "fixed" the drives. Reply
  • Spunjji - Wednesday, August 8, 2018 - link

    Nope, they noted that Samsung fixed the performance issues - which they did. Every article I read on the topic noted that this would still likely affect drives in a power-down state and a couple even tested it. Reply
  • Oxford Guy - Friday, August 10, 2018 - link

    The headlines clearly implied, or (nearly always) directly stated, that Samsung issued "fixes".

    Fixes are not kludgy work-arounds.
    Reply
  • milkywayer - Tuesday, August 7, 2018 - link

    My question is, should I truest this drive with valuable info if endurance can be an issue?

    If the PC is frequently powered On, will it refresh the cells?
    Reply
  • mapesdhs - Wednesday, August 8, 2018 - link

    If you have quite literally "valuable info" then don't use a consumer SSD at all. Heck, damn the speed, you're far better with even a used 840 Pro. That's why I obtained one for this build I did, along with an SM951 for a scratch video drive:

    http://www.sgidepot.co.uk/misc/charitypc1.html
    Reply
  • BurntMyBacon - Wednesday, August 8, 2018 - link

    First point of interest is always have a backup plan. If information is valuable, don't rely on any single copy of it.

    As to your question of endurance, I don't think most personal use cases are likely to have an issue. If you have a professional workload, get a professional drive. The 840 Pro that mapesdhs keeps evangelizing is actually a pretty good option, though a Pro series (MLC) nvme drive will provide better performance while still providing endurance is the same ballpark as the 840Pro.

    As to whether it will refresh the cell if powered on, I would expect most Samsung drive will, though it is not known whether
    Reply
  • BurntMyBacon - Wednesday, August 8, 2018 - link

    As to whether it will refresh if powered on, I don't believe that Samsung flash required the refresh cycle once the moved to 3D NAND with a larger feature size. That said, since QLC halves the voltage swing (and corresponding charge) vs TLC, it is likely that Samsung will need to do something to prevent voltage drift. This may not necessarily require active refreshing, though. It is not known (by me) whether this is a requirement for other manufacturer's 3DQLC NAND either. Reply
  • BurntMyBacon - Wednesday, August 8, 2018 - link

    I get why they don't want an edit feature, but would it really hurt if they added a time limited recall type edit feature for when you fat thumb a hot key that posts your unfinished message before you are done with it. Maybe give you five minutes after a post initiate the edit to catch typos or grammar issues. It wouldn't really be enough to alter a conversation as it is unlikely that others will have responded within this time frame. Reply
  • AbRASiON - Tuesday, August 7, 2018 - link

    Considering the abysmal performance of this thing, I think you really need a $/GB chart on the page and it would be nice to put in a very fast, modern hard drive. Something huge and 7200RPM with a lot of cache on it.

    Just to put it in perspective, because as it stands, wow this thing looks terrible. I expect VERY cheap prices if they're gonna run like this.
    Reply

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