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as ssds or solid-state drives have evolved some of the components have

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become much more sophisticated like the controllers on board that have gone from

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rudimentary single core affairs to multi-core processors with huge amounts

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of RAM and complex algorithms built into their firmware

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but the foundation of nearly every SSD

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the nand flash memory that actually stores your data has actually gotten

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progressively worse in some big ways

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we went from high speed and super reliable slc flash which draws only a

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single one or zero to each cell to dual air mlc to triple layer tlc to finally

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today this is the Intel 660p the first consumer SSD

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with qlc flash which is notable for its

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ability to store 4 bits per cell that

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means 16 separate voltage levels

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this gives it fantastic affordability especially for an NVMe SSD but my mama

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always told me if it seems too good to be true

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it probably is so let's take a look at the pros and

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cons

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for today only you can pick up pc building simulator on chrono.gg for 15

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usd so check it and all of chrono.gg's

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games out at the link in the video description

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let's start with the bad stuff first up is that qlc nand has lower

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endurance than tlc which means that all

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other things being equal it doesn't last for as long

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why well i'm glad you asked because it's

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science time with pictures this is really important

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every time a cell gets written to a voltage pulse is sent through the

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control gate which creates an electric field which agitates the electrons

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causing them to move through the silicon dioxide layer towards the floating gate

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that their layer wears out a tiny bit

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every time a program erase command is sent to the cell causing some of these

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shifting electrons to get stuck inside

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of it which means that it will have and more importantly continue accumulating a

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progressively more negative charge

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now this gets compensated for by applying ever slightly higher positive

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voltage to the cell to get it to the desired voltage state

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now at some point the voltage levels start bordering those required by the

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adjacent states to the point where it takes too long to distinguish what's

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what and that block will get taken out behind the barn old yeller style

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now the fewer layers that there are inside

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of a cell the wider the spare voltage is

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in between the states so then as you can imagine with qlc the point of cannot

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deal with this anymore gg cell comes sooner than with tlc and

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especially mlc or slc much sooner

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second bad stuffs qlc is also slower

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which like wait a second why why is that denser processor

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transistors are better increasing the aerial density of a hard drive platter

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is better shouldn't more data density in nand flash be better

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unfortunately no it's actually the opposite you see with hard drives

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cramming more data into the same surface

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area increases the read and the write speeds because the platter rotates at a

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constant speed usually 5400 to 7200 RPM

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or so which means that the more densely the bits are packed the more of them

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pass under the head in a given amount of time more bits is more data so denser in this

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case is better that is as long as you can keep your read error rate under

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control but that's a whole separate discussion back to ssds for now when an

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SSD cell is accessed a distinction between the multiple voltage levels

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needs to be made and the number of states that you need to sift through

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goes up exponentially with the number of layers that it holds

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so the more layers the more states and

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the longer it takes to get a reading for example it takes 25 microseconds to read

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for slc 50 for mlc 75 for tlc and 100 for qlc

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and it's the same story with rights except the performance drop-off is even

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worse finally big problem number three

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here we're getting into this drive specifically the advertised write speeds

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are kind of hacks because there isn't

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really a right way to do it you see this drive treats part of its qlc cells

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as slc flash as a kind of cache so remember slc

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that's the fastest kind and the exact size of this cache scales depending on

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how much you've filled up your drive so so then

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by this point in the video you're probably thinking all right well then

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qlc has a severe case of the no buenos

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and this here 660p drive is a nomi gusta

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but uh no

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everything that we just said was in theory now it's time for a little bit of

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reality so to put those hacks right numbers to the test and see just how bad

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the whole slc cache with slower qlcnn behind it

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deal affects things we hit this drive with a full range right through hd tune

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pro and guess what halfway through the performance

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plummeted to below that of a hard drive

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and then stayed there for consecutive runs after a brief spike on each run

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but then we observed this behavior only

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after more than half of the drive's capacity was written to something that

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was supposed to happen earlier on in the test which got us thinking

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maybe the caching algorithm was actually working in the background shuffling data

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over to the slower qlc cells so we tried running the cache flusher utility from

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Intel's SSD toolbox during the test and observed its

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progress bar actually going backwards while our benchmark was showing

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throughput spikes when we ran the cash flush after doing a

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full capacity right it took about 20 minutes total and then restored the

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drive to its full write speed now when we tested Intel's own higher

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tier and noticeably more expensive 760p

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we also saw right performance drop during the first run after it ran out of

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cash and dropped further on consecutive runs but

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as you'd expect it remained much faster in the same scenarios than its lesser

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sibling okay so that's synthetic tests but what

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about a real life but edge case

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let's copy a 250 gig steam folder over

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to the 660p there we go same thing it starts off

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fast then it dips dips dips and plummets

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like occ's stock before their bankruptcy in 2013.

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when compared to a similarly priced 840 evo

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that thing managed to maintain a steady 485 megabytes per second

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and completed the copy in only eight minutes and 45 seconds this thing took a

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staggering 23 and a half minutes remember when i said qlc is slow without

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a cache well behold the worst case scenario

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slower than a hard drive meanwhile the tlc equipped 760p after starting off

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strong dropped to a more stable 560 megabytes per second and then maintained

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that completing the same transfer in 8 minutes and 20 seconds now let's get

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more realistic all of the theory crafting we've done so

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far failed to have any tangible effect on

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our other tests game load times were about the same

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between all three drives and when we ran the pc mark 8 storage subsystem bench we

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had to double check that we didn't accidentally test the same drive twice

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so a typical LTT video takes up about 24

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gigs for seven and a half minutes which takes about 20 minutes to render so just

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over one Gigabyte per second of right so we wouldn't have any performance drop

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unless we were filling up our 660p to the brim leaving no room for slc caching

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which by the way we don't recommend filling up any SSD

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also keep in mind that during normal usage your SSD is idle the vast majority

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of the time so that cash flush algorithm will have all the time it needs to

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quietly restore your SSD in the background so now that we've covered the

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worst case for qlc performance and how

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the slc cache can give it boosts of higher performance

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let's talk longevity when compared to Intel's own tlc 760p

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drive this thing is rated for one third the longevity

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but looking closer this actually assumes about a hundred gigabytes of writes per

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day that is basically equivalent to rendering out a couple of LTT videos and

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installing doom on your computer every day

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it's not a realistic use case for the average consumer

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so to sum things up if you were to install a 660p SSD in your system

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unless you're using it for something that it wasn't designed for like as a

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cache for your nas or your hard drive all things considered you would save a

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few bucks since this is Intel we're talking about

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they're not generally known for their aggressive pricing this thing out

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competes other NVMe drives on price and you'd probably never notice that

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you're running qlc because of the slc cash and you'd have a five year warranty

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to give you peace of mind unless of course the drive hits its

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total drive rights limit before that five years runs out so

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the enthusiast in me has some serious misgivings about this move for the nan

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storage industry but

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this product wasn't made for me that's optane

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and i haven't seen anything about this drive to suggest that it won't do a good

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job for its intended audience thanks to the firmware and controller

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trickery that we alluded to earlier

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i guess that's okay even if it makes me uncomfortable

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