The hidden danger of abnormal power failure

If there is no reasonable power-down protection mechanism, and the occurrence of abnormal power-down is inevitable, when abnormal power-down occurs, many problems will be caused.

Lost disk

Abnormal power failure will make the mapping table too late to save, and the mapping of logical addresses to physical addresses will be lost. After the power is turned on again, the SSD will not be recognized by the BIOS. The problem can only be solved by returning to the factory for repair. However, the so-called returning to the factory is to solve the problem of your lost disk by re-opening the card. Re-opening the card also means the loss of all user data!

Loss of data in the cache

SSDs generally use SDRAM or DDR as a cache, where SDRAM is a non-volatile storage medium, and data will be lost after power failure.

An increase in bad blocks leads to misjudgment

In MLC, 2 bits of data can be stored, and the page is stored in the form of a shared page. The two bits of a physical cell of LSB and MSB are mapped to two different pages respectively. The LSB (lower significant bit) is placed on the lower page. Put the MSB (most significant bit) on the upper page for storage. the operation rule is to operate the LSB first and then operate the MSB. Therefore, operations on slow pages take less time than on fast pages.

The principle for SSD power loss protection

Usually, SSDs use tantalum capacitors or super capacitors as power supply devices after power failure. Tantalum capacitors are suitable for wide temperature environments, but have a small capacity. Super capacitors are not suitable for high and low-temperature environments but have a large capacity.

• The super capacitor (or tantalum capacitor) is charged by the normal power supply.

• At the input end of the super capacitor (or tantalum capacitor) and the input end of the SATA power supply, the input power supply is detected respectively, and the detection circuit is connected to the corresponding GPIO port;

• At the moment when the power supply is suddenly cut off, it is fed back to the firmware by GPIO;

• After the port 5V is disconnected, the Firmware feeds back to the HOST, and no longer receives data that has not been transmitted to the SSD;

• The detection circuit at the limit circuit end is fed back to the HOST. The power input is switched, and the power supply is transferred to the super capacitor (or tantalum capacitor) to update the mapping table after power failure and the power required to write data in the cache.

For more information about SSD power loss protection, please contact KingSpec directly.