I figured it would be a good time to dive into SSD's technology and life cycle with the Flash Memory Summit approaching next week. In comparison to conventional hard drives, the SSD datastore is in flash memory chips rather than on a magnetic surface (NAND flash). The SSD is designed to be made with a motherboard, some memory chips (depending on drive size in GB), and an SSD commanding controller.
The SSD memory is non-volatile, that is, even without power, it can maintain data. The data stored in the NAND flash chips can be imagined as an electric load in the cells. In this respect, the question arises: how long does an SSD go on?
The wear and tear of flash memory
The writing procedures wear the memory cells of an SSD and reduce its life. It is well known. But are the memories going to wear out the same way?
There are three different NAND types The memory in flash chips is not all the same:
Single Level Cell (SLC) - One bits of data per cell
Multi-Level Cell (MLC) - Two bits of data per cell
Triple Level Cell (TLC) or 3-bit MLC - three bits of data per cell
You can see: the higher a cell level, the more space bits there are in a cell and the higher the power. Thanks to today's technological advancement, SSDs can store multiple GBs and are affordable. No wonder a recent study reveals that by the end of 2015 the TLC memory form would be equal to approximately 50% of the total NAND chips and that production costs would be around 15% – 20% less than those for MCL chips.
However, the drawback is that adding additional bits to the cells decreases their confidence, resilience, and efficiency. The state (how much space) of an SLC cell is very easy to determine as it is either empty or complete, whereas for MLC cells and TLC cells, as it is more difficult to do the same as for multiple states. A TLC is therefore expected to write four times and read an SLC cell 2.5 times. Saving several bits per cell means speeding up the wear of the NAND memory when addressing the duty life cycle of an SSD.
A floating gate transistor is used to build a memory cell. It is composed of two doors, the control door and the floating door separated by an oxide layer (you can see a schematic representation on the right). The oxide layer which picks electrons on the floating door is worn when operations, e.g. programming and removing the cell, are carried out. As a consequence, an electron drain from the floating door will occur when the oxide layer is weakened.
How long do SSDs last?
This is the question of the million dollars, of course, there is no exact answer, however... Keep reading!
The development of products based on 3-bit MCL (TLC) memory is the trend for SSD. TLC memory starts dominating the SSD market. In common use, 2-bit MLC technology appears to be excessive for durability and efficiency, let alone the SLC with a decreasing and almost completely disappearing requirement. In other words, companies give up an extended life-cycle to reduce the cost to allow flash memory and storage capability to be increased.
However, the length of an SSD appears to be unconcerned. Two powered of 6 drives were able to write operations for two PB of data and all the SSDs that had been tested were able to write hundreds of TB without any problems in an experiment performed by The TechReport on 6 SSDs.
According to the test results, the lifespan of SSD would equal 1000 years (2PB=2000 TB/2TB=1000 years) if 2TB were published every year. We will still be able to use our SSD for years and years and years, even with more knowledge written to them.