Storage Device Rebuild via Garbage Collection Segmentation
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Solution Overview
Problem
The storage device rebuild process in data storage systems, such as RAID or erasure coding architectures, is time-consuming and computationally intensive, leading to significant performance losses and increased latency, which can be mitigated by throttling the rebuild process but at the cost of extended rebuild time.
Innovation Solution
Integrating the storage device rebuild process into ongoing garbage collection operations in a periodic and incremental manner, reducing processing load and data traffic, and utilizing overprovisioned capacity for temporary storage during the rebuild process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the storage device rebuild process is performed at normal speed, then the rebuild time is reduced, but the system performance loss and latency increase significantly
Solution Approach 1:
The rebuild process is segmented into multiple parallel threads, each handling a portion of the data reconstruction. The storage array is divided into multiple stripes, and each stripe can be rebuilt independently by dedicated threads, allowing simultaneous processing of multiple reconstruction tasks without overwhelming the system
Solution Approach 2:
The rebuild process incorporates periodic throttling and pacing mechanisms that regulate the data transfer rate between storage devices. By controlling the timing and rate of read/write operations during rebuild, the system maintains acceptable performance levels while completing reconstruction, preventing sustained high load that would cause significant latency
2Productivity
If the rebuild process is throttled down to 20% of normal level, then the impact on host traffic is reduced, but the rebuild time increases by a factor of 5×
Solution Approach 1:
The rebuild workload is divided into multiple segments handled by parallel threads, allowing the system to process multiple smaller reconstruction tasks simultaneously at moderate speeds rather than one large task at full speed, achieving both performance maintenance and reasonable rebuild time
Solution Approach 2:
The system uses a composite approach combining multiple threads with different priorities and throttling levels, along with overprovisioned capacity as a buffer resource, to create a flexible rebuild mechanism that can adapt to system conditions and maintain performance while completing reconstruction
3Reliability
If the entire dataset is read from all functioning storage devices to rebuild the failed device, then complete data reconstruction is achieved, but the processing load and data traffic become computationally intensive
Solution Approach 1:
Instead of reading entire datasets from all functioning devices simultaneously, the system segments the data into stripe-level portions and processes them in parallel through multiple threads, reducing the peak processing load on any single device or controller while maintaining complete reconstruction capability
Solution Approach 2:
The system extracts only the necessary data portions required for reconstruction from functioning storage devices, using metadata and mapping information to identify and retrieve only the specific data blocks needed for the failed device, rather than reading entire datasets
Data Source
AI summary
Methods and systems for rebuilding a failed storage device in a data storage system. For example, a method including identifying a first garbage collection group (GCG) in a storage array for garbage collection; extracting valid data and redundancy information from functioning storage devices in the storage array associated with the first GCG; reconstructing data of a failed storage device associated with the first GCG based on the extracted valid data and redundancy information from the functioning storage devices associated with the first GCG; consolidating the extracted valid data from the functioning storage devices and the reconstructed data of the failed storage device associated with the first GCG; writing the consolidated extracted valid data from the functioning storage devices and the reconstructed data of the failed storage device associated with the first GCG to a second GCG in the storage array; and reclaiming the first GCG identified for garbage collection.