Modern SSDs offer a much better GB per $ ratio than they used to a few years back.
When SSDs were first making it to market, they were generally in the 64GB or 128GB capacity range.
They were also more expensive than multi-terabyte HDDs.
Things are a little different now, though.
Yes, SSDs are still more expensive per GB than HDDs, but the pricing is much closer.
A 2TB SSD is currently the pricing sweet spot for SSDs.
A 2TB SSD is around twice the price of a 2TB HDD.
you’re free to now get an even more significant performance advantage for that extra cost.
Its still true that if you want many terabytes of storage.
For example, it is cheaper to get HDDs if you want a large RAID array.
But suppose youre only dealing with everyday home-user levels of computer storage.
In that case, a one- or two-terabyte SSD is more than enough and wont break the bank.
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How Did the Price Come Down?
What brought the price down to reasonable levels?
First of all, technology has simply matured.
It gets cheaper to make these things over time.
Some technological breakthroughs and innovations have been a real game-changer, though.
Modern SSDs now generally use TLC flash memory.
TLC stands for Triple-Level Cell, meaning that each memory cell can store three data bits.
These three changes explain the majority of the price improvement in SSDs.
However, there have been plenty of other developments too.
The thing is, TLC comes with some pretty big caveats.
Whats the Problem with TLC?
This slows down the process.
This is a problem because SSDs are supposed to be fast.
Theyve been driving new generations of standards to double and redouble bandwidth to allow speedier storage.
In fact, TLC write speeds are generally somewhere around 2000MBs.
Thats still much faster than an HDD but slower than PCIe 3 SSDs.
Note: TLC isnt the only bang out of flash memory in use.
Write speeds of QLC memory are currently around 350MBs, which is slower than HDDs.
Enter the SLC Cache
SSD manufacturers developed SLC caching to get around these heavily reduced write speeds.
This is a simple trick of writing data to super-fast SLC flash memory.
The data is then copied to the slower TLC flash as fast as possible in the background.
This isnt a problem in most cases but can be if youre making substantial write operations at one time.
For example, restoring or writing a backup typically involves writing to a large percentage of a drive.
The SLC cache typically comes in two distinct parts: a static SLC cache and a dynamic pseudo-SLC cache.
The static cache is generally tiny, less than 10GB even on large 2TB drives.
The static cache is always available, even when the drive is almost full.
Larger SSDs have larger pseudo-SLC caches and can make larger writes at peak speeds.
The dynamic cache size is reduced as the drive is filled up.
Many SSDs allocate about a third of their free space to be used as dynamic SLC cache.
That can be around 600GB on a 2TB drive.
The SSD controller chooses to write incoming data to the SLC cache because it is fast.
This is slower than SLC but faster than TLC.
While SLC caches offer fantastic speeds that MLC couldnt match, MLC would offer twice the cache size.
Then dropping to an MLC cache if more data still needs to be written.
While TLC speeds have been relatively fast, this hasnt been necessary.
As QLC and PLC SSDs become more common, they will come with further write speed reductions.
Secondary MLC caching might be a way the technology develops to alleviate this.
Conclusion
SLC caching is a clever method of write caching on SSDs.
