Memory device, control method for the memory device, and controller
Inventors
Assignees
Kioxia Corp • National Aeronautics and Space Administration NASA
Publication Number
US-8862809-B2
Publication Date
2014-10-14
Expiration Date
2032-08-31
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Abstract
During normal power operation, an erased free block is prepared in nonvolatile memory so that at least one erased free block is continuously available as a standby block. If a power failure occurs, volatile data and its address conversion information are written into the standby block in the nonvolatile memory.
Core Innovation
The invention pertains to a memory device comprising volatile and nonvolatile memories, a controller, and a backup power source designed to secure volatile data during sudden power outages. It involves continuously maintaining at least one erased free block within the nonvolatile memory as a standby block to enable immediate writing of volatile data and associated address conversion information upon detecting a power failure without the need for time-consuming erasure during the outage.
The problem addressed by this invention arises from the limited time provided by typical backup power sources such as capacitors or batteries (often between roughly 10 ms and 0.1 seconds) which is insufficient to erase blocks and then write data during an unexpected outage. Additionally, ongoing error correction during read operations can consume power and time, risking data loss if power fails suddenly. The proposed approach interrupts certain processes such as data reading and error correction on nonvolatile memory when power failure is detected to expedite saving volatile data.
The memory device's controller halts active erasing, writing, garbage collection, and read-modify-write (RMW) processes upon power failure and uses the pre-erased free blocks already prepared during normal operation to quickly write volatile data and management information to the nonvolatile memory. This mechanism ensures that data can be stored safely during a short power backup period and reduces time needed for recovery after power is restored, even when the backup power has limited capacity.
Claims Coverage
The patent contains 4 independent claims centered on memory devices and control methods that maintain erased free blocks for power outage data protection, and on stopping data read during outages.
Continuous maintenance of erased free blocks as standby blocks
The memory device controller continuously maintains at least one erased free block designated for storing volatile memory contents during power outages, ensuring immediate write access without needing to erase blocks after power fails.
Interrupting read processes upon power outage
Upon detecting a power outage, the device interrupts reading data from the nonvolatile memory by allowing completion of the data block currently being read but preventing any further data block reading, thus streamlining outage handling.
Writing volatile memory data to designated erased block during outage
After power failure detection, the controller writes data residing in volatile memory (including management and user data) corresponding to write completions to the designated erased free block for retention during power loss.
Use of multiple designated erased blocks for outage data and control
Multiple blocks are maintained as designated erased free blocks during outages to store various data types including control information indicating completion of power outage recovery, address mapping information, final user data writing, and address conversion information updates.
The independent claims collectively protect the approach of continuously maintaining erased free blocks for outage data storage, interrupting reading during outages to save time, writing volatile data to these pre-erased blocks, and managing multiple such blocks for various recovery and control data to prevent data loss and extend NAND memory endurance.
Stated Advantages
Shortens the time needed to recover from power outages by using a pre-erased free block to immediately store volatile data during power failure conditions.
Enables safe permanent storage of volatile data even with backup power supplies of small capacity by avoiding time-consuming block erasure during outages.
Prevents loss of data by suspending error correction and garbage collection processing during outages, thus minimizing power and processing time required to complete data retention.
Allows reuse of the same erased blocks for repeated outage recovery to prevent write exhaustion of the nonvolatile memory.
Documented Applications
Use as an external memory device such as an SSD connected to a host including personal computers, still or video cameras, or other devices requiring reliable data retention during sudden power outages.
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