Eight terabytes of solid state storage for less than 500 bucks?
Back in 2009, you would have paid that much for a mere 32 gigs of space.
So why is it that you can get 250 times the space for the same price a mere 14 years later?
Well, there's a huge contributing factor you might not know about.
I'm talking about NAND cell performance. You know.
NAND is just a specific type of memory used in SSDs that actually holds your data, and
a cell is the smallest unit of that memory.
Each cell holds a tiny bit of data, between one and five bits each, meaning you'd need
several cells just to store a single letter.
And exactly how many bits a cell can hold has become a crucial differentiator when buying
an SSD. You see, the more bits a cell can hold, the higher the capacity of the drive at the same
cost. But there's a trade-off. More bits per cell also means less longevity and less speed.
In other words, the drive will wear out faster. These things happen because more bits are written over all to each cell, shortening
their lifespan, and the additional bits means it takes longer for the drive to figure out
exactly what data needs to read from or be written to each cell.
This higher data density also means that the error rate can increase.
This is because temperature fluctuations can cause electron leakage in tightly packed cells,
so the controller chip of the drive has to perform more error-correcting functions, slowing
the drive down even more. Come on!
But, spoiler alert, using more bits per cell is the primary way we're getting bigger,
cheaper drives. So how the heck are we making up for their speed shortcomings?
One very common method is caching, which can be done in two ways.
One by using high-speed DRAM on the SSD, similar to what you'd find in your main system memory.
Or two, by treating a small portion of the drive as fast, one-bit, single-level cells
or SLCs by only writing one bit to each cell, even if it can hold more.
I can do more, coach! Put me in! For operations that can be completed in short bursts, the SSD will make use of one of these
kinds of cache to keep speeds high. The transfer rates only drop if large amounts of data have to be moved, resulting in the
cache filling and the drive having to fall back onto slower MLC, TLC, or QLC cells.
That's short for multi-level, triple-level, and quad-level, respectively, which can hold
two, three, or four bits a piece. And some lower-end drives even use some of your PC's main memory as cache to leverage
the benefits of faster memory without adding cost to the drive itself.
Another strategy is simply to stack NAND cells on top of each other to increase data density
rather than going to a higher and slower level of cell.
This has been heavily marketed by Samsung in particular as VNAND technology, where the
V stands for vertical. As in, sick vert, bro.
But how far can we go in terms of cramming more bits into one cell while still keeping
speeds reasonable? Well, it looks like PLC, or Penta-level cell SSDs, are on their way and might appear in
2025. But as you can probably figure out, each time you add another bit, you see more and more
of a diminishing return in terms of performance overhead and relative capacity, resulting in
PLC only giving you a 25% increase in storage.
And because of the complexity inherent in increasing capacity up to five bits per cell,
the drives will need new controller chips, hence the delay in getting PLC SSDs to market.
And once they do arrive, they might not be all that great for folks who need to write
to them often, such as content creators or gamers who frequently change up the titles
stored in their local drives. That's the longevity concern we touched on earlier, which, unlike speed, may not be
figured out by the time PLC drives hit store shelves.
But still, PLC NAND should be a way to store unprecedented amounts of data cheaply, unless
you're willing to go back to old-school mechanical hard drives.
I do kind of miss the little click-clack noises they make.