In this article we further explain some of the intricacies of SSD - Solid State Drive - technology and terminology.
When you first delve into SSD’s you are likely bewildered by the various acronyms, numbers and specifications.
In this article HomeKit Australia explains dome of the various data recording formats employed on different SSD’s.
SLC SSD’s - the Single-Level Cell
SLC is the most rudimentary type of SSD. It is the single-level cell SSD.
This SSD is the fastest and most durable type of SSD but they accept only one bit per memory cell. The bottom line is that SLC SSD’s are less error-prone and generally the most reliable SSD.
Typically SLC SSD’s are considerably more expensive than other SSD’s and are reserved for enterprise applications.
MLC SSD’s - Multi-Level Cell
The description Multi-Level Cell is somewhat misleading as MLC SSD’s only store two bits per cell.
MLC SSD’s are marginally slower than SLC SSD’s. That’s simply because it takes extra time to write two bits onto a cell than just the one, as is the case with SLC SSD’s.
MLC SSD’s also suffer somewhat in durability and reliability as data is written to the NAND flash more often than with an SLC SSD.
Despite this MLC SSD’s offer a good combination of performance and reliability.
TLC SSD’s - Triple-Layer Cell
Also known as 3D NAND, TLC SSD's write three bits to each cell and are the most commonly available SSD in the consumer market.
Typically they offer higher capacities and smaller physical size than both SLC and MLC SSD’s.
The downside for TLC SSD’s come via lower speeds, reliability and durability. This isn’t all bad as manufacturers work hard to improve all aspect of TLC SSD’s.
For example, HomeKit Australia’s upcoming SSD’s utilise Triple Layer Cells and incorporate a premium controller from Silicon Motion that significantly improves speed, reliability and durability of the SSD technology.
A TLC SSD can be expected to be totally reliable for many years and this is improving all the time.
When buying any SSD always pay close attention to the TBW number that is explained below.
QLC SSD’s - Quad-Level Cell
As you might expect, QLC SSD’s can write four bits per cell.
Whilst QLC SSD’s can cram in much more data than other SSD’s, their performance and durability is much lower than the other SSD’s.
This is improving all the time and is generally acceptable in non high-performance situations such as home use.
PLC SSD’s - Penta Level Cell
Still somewhat in their infancy, PLC SSD’s write 5 bits per cell.
They are yet to be common place in the consumer market with manufacturers working to improve performance and durability.
WLT - Wear Levelling Technology
It is worth remembering that SSD cells begin degrading as soon as they’re used.
In order to help keep drives in best condition for the longest amount of time, SSD manufacturers began to include wear technology.
Simply this means that on a modern SSD data is written to memory cells as equally as is possible. Rather than writing a certain block in one section of the SSD all the time, your SSD will distribute data evenly across all the cells. The aim is to access and fill the cells at relatively the same rate.
Terabytes Written (TBW)
Typically, SSD durability is expressed as TBW or terabytes written. This is the conservative number of terabytes that can be written before an SSD can be expected to fail.
TBWs are “safe level” estimates; Good quality SSD’s can be expected to safely exceed the TBW limits.
Remember, always have a logical, safe backup strategy - no matter what type of data storage you employ.
NAND manufacturers have placed NAND memory cells much closer together on a flat surface to make their drives smaller but with higher capacity. This had some level of success but flash memory starts to lose its reliability when the cells are too close together.
To bypass this limitation the manufacturers stacked the memory cells on top of each other to increase capacity.
This is what is now commonly called 3D NAND or vertical NAND.
All SSD’s utilise caching.
Caching briefly stores data before it is written to the SSD. Caches are crucial to boosting SSD performance. In any SSD, caches will be built of SLC and/or MLC NAND.
If your SSD cache fills, expect performance to drop significantly. This is especially true of TLC and most QLC drives.
The fastest interface presently available, NVMe SSD’s access a computer’s motherboard via PCIe if installed internally or externally via Thunderbolt 4 technology.
The blazing speeds of Thunderbolt NVMe SSD drives are at least three times faster than SATA III.
m.2 describes the physical size, shape, and design of an NVMe SSD.
m.2 NVMe SSD’s resemble a common RAM DIMM. They fit into special slots on most modern computer motherboards and external cases such as Thunderbolt enclosures.
If you see a number like 2280 or 2260, it refers to the length of the SSD in mm.
The is the most common hard drive and SSD interface around.
Remember SATA III has a maximum throughput of 600MB per second, and significantly slower than Thunderbolt.
HomeKit Australia stocks a Thunderbolt docking station that will also house either an NGFF or our preferred NVMe SSD.