as ssds or solid-state drives have evolved some of the components have
become much more sophisticated like the controllers on board that have gone from
rudimentary single core affairs to multi-core processors with huge amounts
of RAM and complex algorithms built into their firmware
but the foundation of nearly every SSD
the nand flash memory that actually stores your data has actually gotten
progressively worse in some big ways
we went from high speed and super reliable slc flash which draws only a
single one or zero to each cell to dual air mlc to triple layer tlc to finally
today this is the Intel 660p the first consumer SSD
with qlc flash which is notable for its
ability to store 4 bits per cell that
means 16 separate voltage levels
this gives it fantastic affordability especially for an NVMe SSD but my mama
always told me if it seems too good to be true
it probably is so let's take a look at the pros and
cons
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let's start with the bad stuff first up is that qlc nand has lower
endurance than tlc which means that all
other things being equal it doesn't last for as long
why well i'm glad you asked because it's
science time with pictures this is really important
every time a cell gets written to a voltage pulse is sent through the
control gate which creates an electric field which agitates the electrons
causing them to move through the silicon dioxide layer towards the floating gate
that their layer wears out a tiny bit
every time a program erase command is sent to the cell causing some of these
shifting electrons to get stuck inside
of it which means that it will have and more importantly continue accumulating a
progressively more negative charge
now this gets compensated for by applying ever slightly higher positive
voltage to the cell to get it to the desired voltage state
now at some point the voltage levels start bordering those required by the
adjacent states to the point where it takes too long to distinguish what's
what and that block will get taken out behind the barn old yeller style
now the fewer layers that there are inside
of a cell the wider the spare voltage is
in between the states so then as you can imagine with qlc the point of cannot
deal with this anymore gg cell comes sooner than with tlc and
especially mlc or slc much sooner
second bad stuffs qlc is also slower
which like wait a second why why is that denser processor
transistors are better increasing the aerial density of a hard drive platter
is better shouldn't more data density in nand flash be better
unfortunately no it's actually the opposite you see with hard drives
cramming more data into the same surface
area increases the read and the write speeds because the platter rotates at a
constant speed usually 5400 to 7200 RPM
or so which means that the more densely the bits are packed the more of them
pass under the head in a given amount of time more bits is more data so denser in this
case is better that is as long as you can keep your read error rate under
control but that's a whole separate discussion back to ssds for now when an
SSD cell is accessed a distinction between the multiple voltage levels
needs to be made and the number of states that you need to sift through
goes up exponentially with the number of layers that it holds
so the more layers the more states and
the longer it takes to get a reading for example it takes 25 microseconds to read
for slc 50 for mlc 75 for tlc and 100 for qlc
and it's the same story with rights except the performance drop-off is even
worse finally big problem number three
here we're getting into this drive specifically the advertised write speeds
are kind of hacks because there isn't
really a right way to do it you see this drive treats part of its qlc cells
as slc flash as a kind of cache so remember slc
that's the fastest kind and the exact size of this cache scales depending on
how much you've filled up your drive so so then
by this point in the video you're probably thinking all right well then
qlc has a severe case of the no buenos
and this here 660p drive is a nomi gusta
but uh no
everything that we just said was in theory now it's time for a little bit of
reality so to put those hacks right numbers to the test and see just how bad
the whole slc cache with slower qlcnn behind it
deal affects things we hit this drive with a full range right through hd tune
pro and guess what halfway through the performance
plummeted to below that of a hard drive
and then stayed there for consecutive runs after a brief spike on each run
but then we observed this behavior only
after more than half of the drive's capacity was written to something that
was supposed to happen earlier on in the test which got us thinking
maybe the caching algorithm was actually working in the background shuffling data
over to the slower qlc cells so we tried running the cache flusher utility from
Intel's SSD toolbox during the test and observed its
progress bar actually going backwards while our benchmark was showing
throughput spikes when we ran the cash flush after doing a
full capacity right it took about 20 minutes total and then restored the
drive to its full write speed now when we tested Intel's own higher
tier and noticeably more expensive 760p
we also saw right performance drop during the first run after it ran out of
cash and dropped further on consecutive runs but
as you'd expect it remained much faster in the same scenarios than its lesser
sibling okay so that's synthetic tests but what
about a real life but edge case
let's copy a 250 gig steam folder over
to the 660p there we go same thing it starts off
fast then it dips dips dips and plummets
like occ's stock before their bankruptcy in 2013.
when compared to a similarly priced 840 evo
that thing managed to maintain a steady 485 megabytes per second
and completed the copy in only eight minutes and 45 seconds this thing took a
staggering 23 and a half minutes remember when i said qlc is slow without
a cache well behold the worst case scenario
slower than a hard drive meanwhile the tlc equipped 760p after starting off
strong dropped to a more stable 560 megabytes per second and then maintained
that completing the same transfer in 8 minutes and 20 seconds now let's get
more realistic all of the theory crafting we've done so
far failed to have any tangible effect on
our other tests game load times were about the same
between all three drives and when we ran the pc mark 8 storage subsystem bench we
had to double check that we didn't accidentally test the same drive twice
so a typical LTT video takes up about 24
gigs for seven and a half minutes which takes about 20 minutes to render so just
over one Gigabyte per second of right so we wouldn't have any performance drop
unless we were filling up our 660p to the brim leaving no room for slc caching
which by the way we don't recommend filling up any SSD
also keep in mind that during normal usage your SSD is idle the vast majority
of the time so that cash flush algorithm will have all the time it needs to
quietly restore your SSD in the background so now that we've covered the
worst case for qlc performance and how
the slc cache can give it boosts of higher performance
let's talk longevity when compared to Intel's own tlc 760p
drive this thing is rated for one third the longevity
but looking closer this actually assumes about a hundred gigabytes of writes per
day that is basically equivalent to rendering out a couple of LTT videos and
installing doom on your computer every day
it's not a realistic use case for the average consumer
so to sum things up if you were to install a 660p SSD in your system
unless you're using it for something that it wasn't designed for like as a
cache for your nas or your hard drive all things considered you would save a
few bucks since this is Intel we're talking about
they're not generally known for their aggressive pricing this thing out
competes other NVMe drives on price and you'd probably never notice that
you're running qlc because of the slc cash and you'd have a five year warranty
to give you peace of mind unless of course the drive hits its
total drive rights limit before that five years runs out so
the enthusiast in me has some serious misgivings about this move for the nan
storage industry but
this product wasn't made for me that's optane
and i haven't seen anything about this drive to suggest that it won't do a good
job for its intended audience thanks to the firmware and controller
trickery that we alluded to earlier
i guess that's okay even if it makes me uncomfortable
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