Virtual Timer for SSD Data Retention Using RBER
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Solid state drives (SSDs) face challenges in data retention reliability due to inaccurate data age recording, which can lead to data loss, especially when power outages affect system clocks and temperature variations accelerate data degradation, necessitating a more accurate timing mechanism to refresh data before it becomes unreliable.
Innovation Solution
Implementing a virtual timer that estimates data age by calculating the raw bit error rate (RBER) and accounting for temperature acceleration, allowing for periodic data refresh based on a defined retention time threshold, even in the absence of a temperature profile, using single-level cell (SLC) memory blocks to enhance data reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If system clock is used to track data age, then timing mechanism is simple, but data age recording becomes inaccurate during power outages
Solution Approach 1:
The patent introduces virtual timing data as an intermediary between the system clock and the data retention mechanism. This virtual timer stores timing information in non-volatile memory, allowing it to persist across power outages and provide accurate data age tracking without requiring continuous power or complex real-time clock circuits.
Solution Approach 2:
The patent creates a copy of the timing function by implementing a virtual timer that mimics system clock behavior but stores its state in non-volatile memory. This virtual copy continues timing operations even when the actual system clock loses synchronization due to power loss, thereby maintaining measurement accuracy.
2Reliability
If data refresh is performed frequently to ensure retention, then data reliability improves, but write operations increase reducing SSD lifespan
Solution Approach 1:
The patent performs preliminary action by accurately tracking data age using the virtual timer and proactively refreshing data before it becomes unreliable. By monitoring the virtual timer values and refreshing data just before the retention threshold is reached, the system avoids both premature refreshes (wasting writes) and late refreshes (losing data), thereby optimizing SSD lifespan while maintaining reliability.
3Measurement precision
If temperature acceleration is accounted for in data age calculation, then data retention accuracy improves, but calculation complexity increases
Solution Approach 1:
The patent applies parameter changes by adjusting the virtual timer values based on temperature acceleration factors. The system modifies the effective data age calculation by applying acceleration multipliers derived from temperature measurements, allowing accurate retention timing without requiring complex real-time modeling of degradation physics.
Data Source
AI summary
Approaches, techniques, and mechanisms are disclosed for improving data retention using a virtual timer. A memory controller may use a raw bit error rate (RBER) to find an equivalent temperature-accelerated data age of a data item. The data age is computed by using the initial RBER of virtual timing data (VTD) as a virtual write in time of the data item compared to a present time using the current RBER of the VTD. When the data age is determined to exceed a data retention threshold, a data refresh is performed on the data item at the memory block on the memory device. The data age may be stored as virtual timing data on the memory block.