SSD Write Rate Control via Dynamic Sub-device Metering
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Solution Overview
Problem
Non-volatile storage devices like SSDs have limited write cycles, and existing wear-leveling technologies may not effectively manage write rates to ensure the devices meet their specified lifetimes, potentially leading to premature wear and reduced performance.
Innovation Solution
A method that calculates and controls the write rate to sub-devices over time periods to ensure the overall write rate does not exceed the specified limit, using equations to determine the write rate and accumulate credits during low activity periods for use during high activity periods, allowing for flexible write rate management and peak write allowances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If wear-leveling technology is used to distribute writes across cells, then device lifetime is extended, but write expansion factor increases reducing effective write capacity
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the write rate to each sub-device and comparing it against calculated allowed write rates. The system adjusts write operations in real-time based on this feedback, ensuring that the cumulative write rate does not exceed the specification while distributing writes evenly across sub-devices to extend device lifetime.
Solution Approach 2:
The patent dynamically adjusts the write rate to each sub-device based on its current wear state and the overall device write rate. The allowed write rate Wa,a is calculated dynamically using the formula that considers the specification Wspec, current wear Wa,total, and remaining lifetime Ta, allowing the system to adapt write distribution strategies in real-time to optimize both lifetime extension and write capacity utilization.
2Duration of action of stationary object
If write rate is strictly controlled to meet specification, then device lifetime is guaranteed, but peak write performance is reduced
Solution Approach 1:
The patent allows temporary excessive write rates to individual sub-devices when the overall device write rate remains within specifications. The system calculates the allowed write rate Wa,a for each sub-device based on its current wear state, permitting some sub-devices to receive more writes than their strict average share would suggest, as long as the cumulative effect does not violate the overall specification Wspec. This partial relaxation enables peak performance while maintaining lifetime guarantees.
Solution Approach 2:
The patent changes the parameter control approach from fixed per-subdevice write limits to dynamic allowed write rates Wa,a that are recalculated based on current device state. The formula Wa,a = (Wspec - Wa,total) / (Ta + tb) allows the system to adjust write rate parameters in real-time, enabling higher write rates during periods when the device has remaining capacity and lower rates when approaching limits, thus maintaining both lifetime guarantees and peak performance capability.
3Stability of the object's composition
If uniform write distribution is applied to all sub-devices, then wear is evenly spread, but flexibility in handling varying write patterns is reduced
Solution Approach 1:
The patent applies local quality by allowing different write rates to different sub-devices based on their individual wear states Wa,a and remaining capacities. Instead of uniform distribution, the system calculates and enforces sub-device-specific allowed write rates Wa,a using the formula that considers each sub-device's contribution to overall wear Wa,total. This enables the system to adapt write distribution to local conditions while maintaining overall device lifetime guarantees.
Solution Approach 2:
The patent performs preliminary calculation of allowed write rates Wa,a for each sub-device before executing write operations. By pre-calculating the maximum allowable write rate for each sub-device based on current wear state and specification limits, the system prepares write rate budgets in advance that guide subsequent write operations. This preliminary action enables flexible adaptation to varying write patterns while ensuring wear distribution remains within safe limits.
Data Source
AI summary
The number of writes to a device ("D1-n") consisting of n sub-devices ("Da") is counted: [ W 1 , 1 ... W 1 , m - 1 W 1 , m W 2 , 1 ... W 2 , m - 1 W 2 , m ... ... ... ... W n , 1 ... W n , m - 1 W n , m ] where: Wa,b is the number of writes to sub-device Da in time period "b"; n>1; m>1. A write rate is determined for each sub-device Da at the end of time period p ("WRa,p") using the following equation: WR a , p = ∑ b = 1 p W a , b ∑ b = 1 p t b where: tb is the amount of time in time period "b"; p<m. The write rate to sub-device Da is controlled in time periods after time period p so that device D1-n will have a guaranteed lifetime ("LD1-n").