SSD RAID Redundancy via Over-provisioned Capacity
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Solution Overview
Problem
In solid state storage systems using RAID redundancy, practical replacement of failed storage elements is often impractical and costly, necessitating an alternative method to restore redundancy and user data protection.
Innovation Solution
Utilizing the over-provisioned capacity within the storage device to rebuild RAID redundancy by reducing stripe size and reallocating spare capacity, allowing for data recovery without the need for physical replacement of failed elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If physical replacement of failed storage elements is implemented, then data redundancy is restored, but cost and complexity increase significantly
Solution Approach 1:
The patent creates a logical copy of the failed storage element's data using parity information from remaining elements. Instead of physically replacing the failed element, the system reconstructs the data virtually through parity calculations, thereby restoring redundancy without physical intervention or additional spare elements.
Solution Approach 2:
The system uses its own existing resources (remaining storage elements and parity information) to restore redundancy after failure. The surviving elements collectively perform the reconstruction function that would otherwise require dedicated spare elements, making the system self-sufficient for fault recovery.
2Reliability
If over-provisioned capacity is used to restore redundancy, then system reliability is maintained, but available user capacity decreases
Solution Approach 1:
The system dynamically reallocates storage capacity based on failure conditions. During normal operation, over-provisioned capacity remains available for potential expansion or additional redundancy. Upon failure, this same capacity is dynamically converted into active redundancy resources, and the stripe configuration is adjusted to reflect the new operational state.
Solution Approach 2:
The patent changes the operational parameters of storage elements from user-accessible capacity to redundancy-providing capacity. By modifying the functional state of over-provisioned sectors and adjusting stripe sizes, the system transforms available capacity into active parity resources needed for fault tolerance.
Data Source
AI summary
Redundant “parity” RAID (5, 6, 50, 60) is a well-known technique for increasing data reliability beyond the failure rate of an individual storage device. In many implementations of redundant RAID, when a storage element is lost, a replacement or spare element is required to restore redundancy. A typical solid state storage device is over-provisioned with more storage media than is required to satisfy the specified user capacity. Embodiments of the present invention utilize the additional over-provisioned capacity and potentially modify the stripe size to restore RAID redundancy when a storage element or path (i.e., page, block, plane, die, channel, etc.) has failed. In some cases, this may also involve reducing the RAID stripe size.