Non-blocking coherent re-writes for storage defragmentation
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Solution Overview
Problem
Fragmentation of memory in storage systems reduces performance over time, leading to decreased efficiency, and existing defragmentation methods can cause data inconsistencies and increased write amplification.
Innovation Solution
A non-blocking coherent re-write process is implemented, where the storage system takes a snapshot of the logical-to-physical address table during a read operation and compares it with the current version during a write operation, ensuring data coherency and only writing data back if unchanged, thereby maintaining logical and physical address mapping coherency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If traditional defragmentation operations are performed, then memory fragmentation is reduced, but data inconsistencies and increased write amplification occur
Solution Approach 1:
The system performs a read operation first to obtain a snapshot of the logical-to-physical address table before the defragmentation write operation. This preliminary action allows the system to compare address mappings before writing, preventing data inconsistencies by ensuring the write target is still valid and unchanged.
Solution Approach 2:
The system compares the snapshot of the logical-to-physical address table with the current version after the read operation. This feedback mechanism allows the system to detect changes in address mappings and decide whether to proceed with the write operation, thereby maintaining data consistency while reducing fragmentation.
2Stability of the object's composition
If defragmentation operations are performed, then memory fragmentation is reduced, but write amplification increases
Solution Approach 1:
By performing the read operation first and obtaining a snapshot of the address table, the system can later compare this snapshot with the current state before writing. This allows the system to identify whether the data has actually changed and only write when necessary, reducing unnecessary write operations and thus write amplification.
Solution Approach 2:
The system uses its own read operation to gather information about the current state of the memory mapping, then uses this information to make intelligent decisions about whether to perform the write operation. This self-service approach allows the defragmentation process to be more efficient and reduce redundant writes.
3Reliability
If read operations are performed to check data coherency, then data consistency is maintained, but read performance may be impacted
Solution Approach 1:
The read operation to obtain the address table snapshot is performed as a preliminary action before the defragmentation write. By batching this read operation with the subsequent write operation and using the snapshot for comparison, the system minimizes the impact on read performance while ensuring data coherency is maintained throughout the defragmentation process.
Data Source
AI summary
A host sends a storage system a command to read data from a memory and then a command to write the data back to the memory to defragment the data. The host sends flags along with the commands. The flag sent with the read command causes the storage system to take a snapshot of the logical-to-physical address map relevant to the data. The flag sent with the write command causes the storage system to compare the snapshot with the current version of the logical-to-physical address map and write the data back to the memory only if there is a match.