Understanding SSD | HomeKit Australia

Understanding SSD

Headed into 2021 a major focus of the HomeKit Australia online store is on Thunderbolt and SSD technologies .... and as HomeKit Australia is about to begin shipping its own NVMe SSD's, we thought we would share some more about the superiority of NVMe SSD's and why we use and sell them.

It is easy to be confused when you first start delving into Solid State Drives or SSD's. There's various acronyms, numbers and specifications, which at first mean close to nothing.

First up, let's look at the various cell structures of different SSD's. You will see terms like triple layer or 3D or 4D NAND, so let's take a peek.

First up there's .....

SLC SSD’s or Single Level Cell

The SLC is the most rudimentary type of Solid State Drive.

Very simply, this is the single-level cell SSD. An SLC SSD is the fastest and most durable type of SSD but they accept only one bit per memory cell.

Bottom line is that SLC SSD’s are less error-prone and generally the most reliable SSD, but also the most expensive. Because SLC SSD’s are considerably more expensive than other SSD’s and are reserved for enterprise applications.

MLC SSD’s or Multi-Level Cell

Calling this SSD a Multi-Level Cell is a little misleading as MLC SSD’s only store two bits per cell, plus MLC SSD’s are marginally slower than SLC SSD’s.

That’s down to it taking extra time to write two bits onto a cell than just one .... as is the case with SLC SSD’s. 

With data being written to the NAND flash more often than with an SLC SSD, MLC SSD’s also suffer somewhat in durability and reliability.

Shortcomings aside, MLC SSD’s offer a good combination of performance and reliability. 

TLC SSD’s or Triple-Layer Cell

3D NAND or TLC SSD's write three bits to each cell and are typically what you will buy online and in the shops. 3D NAND dominates the consumer market SSD.

3D NAND generally offer higher capacities and smaller physical size than both SLC and MLC SSD’s.

Initially, the downside for 3D NAND comes in slightly lower speeds, reliability and durability. This isn’t all bad as manufacturers work hard to improve all aspect of TLC SSD’s.

In particular, manufacturers of the controller chips than essentially run an SSD now have available technologies that significantly reduce the shortcomings of writing 3 bits to each cell.

For example, HomeKit Australia’s new 1TB and 2TB SSD’s utilise 3D NAND and incorporate a premium controller from Silicon Motion (SMI) that significantly boosts speed, reliability and durability of these SSD's.

3D NAND 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 or Quad-Level Cell

You've probably already guessed .... QLC SSD’s 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 previously described SSD’s.

Whilst this is improving all the time, QLC SSD's are generally acceptable in non high-performance situations such as home use.

HomeKit Australia use QLC SSD's in their SATA III 2.5" SSD's. The use of QLC enables us to lower the price on a product that does not enjoy the blinding speeds of PCIe and Thunderbolt data transfer.

PLC SSD’s - Penta Level Cell

With limited availability, 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.

Expect to see more PLC SSD's in 2022.

Additionally cells further developed through cell stacking, especially ....


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.


There are several technologies either specific or associated with Solid State Drives that are also extremely important to understand. The first is .......

WLT - Wear Levelling Technology

Not many people will tell you this, but Solid State Drive cells begin degrading as soon as they’re used. It's a bit like buying a new car except with SSD's great new technologies like Wear Levelling Technology, come to your rescue.

So that an SSD stays in optimal condition for the longest period of time, SSD controller manufacturers began to include wear technology to minimise the writing of data to aligned cells and maximise the life of the Solid State Drive.

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 billions of cells.

The aim of WLT is to access and fill the cells at relatively the same rate.

WLT has allowed lower cost 3D and 4D SSD's to offer significantly improved expected lives. Our HomeKit Australia NVMe SSD's offer greater than 20 year data retention.

Newer SSD's will also offer a multi-year warranty so manufacturers have become extremely confident in the ability of on-board controllers from companies like SMI (Silicon Memory) to significantly extend the life cycle of all Solid State Drives.

Terabytes Written (TBW)

SSD durability is expressed as TBW or terabytes written.

TBW is the conservative number of terabytes that can be written before an SSD can be expected to fail.

TBWs are “safe level” estimates and good quality SSD’s can be expected to safely exceed the TBW limits. 

For example HomeKit Australia's NVMe SSD's have a MTBF (mean time between failure) rating of over 1 million hours. 1TB NVMe SSD's and 2TB NVMe SSD's from HomeKit Australia come standard with a 3 year warranty.

Remember, always have a logical, safe backup strategy - no matter what type of data storage you employ.


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.

Additionally, there are some more SSD terminologies that are important to understand.


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. Typically the NVMe that is sold by HomeKit Australia and others is generally 2280 NVMe.


The fastest interface presently available, NVMe SSD’s access a computer’s motherboard via PCIe if installed internally or externally via Thunderbolt 4 or USB4 technologies. 

The blazing speeds of Thunderbolt NVMe SSD drives are at least three times faster than SATA III.

HomeKit Australia recommends and uses themselves NVMe SSD's and sells a range of SSD's and Thunderbolt products that contain NVMe SSD's.

HomeKit Australia also stocks a Thunderbolt docking station that will also house two NVMe SSD's.



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.

At HomeKit Australia we use 2.5" SSD's as essentially a legacy product that can improve the performance and extend the life of existing computers.

At HomeKit Australia we love Solid State Drives and the Thunderbolt interface and take real satisfaction in bringing new Thunderbolt products to market. HomeKit Australia is 100% Australian owned and operated and we use every Thunderbolt product we sell, ourselves ..... thanks for stopping by our Thunderbolt online store.