Flash memory test Reliability study
Renice r-Backup® Power Failure Protection of SSD
2019-04-09 ERIC

rBackup (Rapid Backup) refers to a technique of how to flush data stored in DDR into NAND Flash within a very short period. It is developed by Renice to solve the problem that regular power failure protecting mechanism (based on super capacitor or tantalum capacitor) does not work when capacitor ages with power less than initial design as time goes by.


Background:

Mainstream SSD deploy SDRAM or DDR to improve the R/W speed. That follows the issue of data loss or mapping table loss when sudden power failure occurs. To guarantee the data integrity, usually SSD makers design a power failure protecting mechanism based on Super-Capacitor or Tantalum Capacitor, which will work as backup power for SSD in power failure circumstance.

This design seems to be perfect to balance the performance and reliability. However there is a potential hazard behind it in real application. Both Super-Capacitor and Tantalum Capacitor keep aging as charge & discharge times increase. Common warranty period from SSD makers is 3 to 5 years, which apparently does not take this problem into account.

Let's assume that the left power of Tantalum Capacitor becomes only 50% of initial design as it ages. Then is it enough to power the SSD to write all data in SDRAM into NAND Flash? If the answer is no, it might cause damages to SSD as below.


1. Mapping Table under updating is lost and whole SSD crashes. 

2. Data stored in SDRAM is lost.


3. If frequent power-failure happens, False add-on Bad Block will significantly increase.

These issues are all threats to SSD reliability, which cannot be accepted by critical applications.

To get rid of such potential hazards, Renice developed rBackup technique, based on which the time taken to write data in DDR into NAND Flash is shortened by 50%~70% as before. And Renice has already acquired patent of invention on this method, named as [A technique and system to implement quick backup of SSD data under abnormal power failure circumstance].

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