How SSD Technology Keeps Getting WORSE! - Intel 660p Review
Linus Tech Tips
·Linus Tech Tips
·2019-05-06
·
1,864 words · ~9 min read
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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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