PLP is the all-important mechanism to protect data stored in an SSD during a power outage, which is critical in an SSD’s reliability. Data, commands, and reflective tables are temporarily stored in DRAM. A rapid response time is an advantage in an SSD’s performance however, since DRAM is volatile memory, it requires an external power source to maintain operationability. When the system is properly shut down, the Host end will issue a command to the SSD controllers to notify the subsequent power interruption, which allows the response time for SSD to refresh cache and revise Mapping Table while saving the data temporarily-stored in DRAM to NAND Flash. However, when the system power is down without warning, the data in cache and Mapping Table cannot be refreshed and stored in NAND Flash. As a result, the SSD data may not be correctly updated, become incompatible, and data loss, or even equipment damage may follow.
- Transmit data in use or cache in the DRAM to NAND Flash
- Maintain the integrity of SSD Mapping Table. This table records data logic and Logical page number to Physical page number Table and incomplete or erroneous Mapping Table could cause disc swap.
PLP can backup key data through firmware and restore the last backup prior to power down. The upside of this method is that it allows the preservation of the correct data, but the downside is that some data from the latest backup to the power down may still be lost.
The PLP mechanism is based on the firmware design is commonly used in consumer-grade SSDs while it is a hardware and software design for industrial and enterprise-class SSDs. This helps provide more effective power down data protection, with Hi-C Cap or Super Cap to supply power, in order to prolong the SSD operating times after power down.