What is NAND Flash?

NAND flash memory is a type of non-volatile storage technology that does not require power to retain data.

Where is it used?

Primarily found in Memory Cards, USB Flash Drives, Solid State Drives for storage and transfer of data.

What are the devices used for?

Typical Data logging and Recording Advanced Data Logging and Recording (device collects data but also wirelessly communicates alarming events) Data storage and transfer Boot Devices

Why is it used?

Devices made using NAND Flash offer mechanical shock resistance, high durability and are able to withstand high pressure and temperature when compared to traditional hard disk drives. NAND also offers fast read access times.

What are the limitations?

NAND has a finite number of read/write cycles in a specific block each time a bit is written or erased constitutes a program/erase cycle. Once a device reaches the user and is in operation (After manufacturer early life failure tests) its first day is always it best. NAND failure is inevitable once the program erase cycles are reached. Individual cells fail and overall performance degrades, a concept known as wear-out.

Why is this important?

When the NAND fails the device becomes unusable resulting in the loss of data and application functionality.

How can I prevent this happening?

The simple answer is you can’t! Advanced wear leveling, over provisioning and firmware algorithms can all help to increase NAND endurance however the best method is to understand your data usage and what the limitations are of each type of NAND used (coupled with clever endurance technology) you can protect your applications functionality and data. 

What NAND types are there and what are the limitations?

Single Level Cell (SLC) 60-100K Program / Erase Cycles Pseudo Single Level Cell (pSLC) 20-30K Program / Erase Cycles Multi Level Cell (MLC) 1-3K Program / Erase Cycles Triple Level Cell (TLC)

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Which one is right for my application?

Each application will have different demands on endurance, temperature, performance and data retention so it will depend on which criteria are most important. The general rule is for industrial applications where quality, reliability and longevity of supply are required SLC, pSLC or industrial grade level MLC are used. For consumer based technology where the impact of losing functionality or data are not severe devices are typically thrown away and replaced due to the low cost. These will always use MLC or TLC.

 

NAND endurance and Bit Error Rate (BER) Trends

 

I understand but…..

The consumer card I bought years ago still works today, why can’t I use these in an application that needs reliability? The use of NAND globally is dominated by consumer and enterprise applications. The pressures to increase capacity and reduce costs are phenomenal. As NAND is produced in wafer form this is achieved by shrinking the geometry of the NAND in order to yield more NAND chips per wafer. The trade off is Endurance and Data Retention , 5 years ago an MLC NAND would have offered 10K + program erase cycles. Today it is 1K so they last a 10th of the time and the reliality is your application is a lot more data intensive than your camera or home computer. So this will be realised much sooner.

Still have questions?

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