Flash Translation Layer Lookaside Table Defragmentation
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Solution Overview
Problem
File-system fragmentation in solid-state drives (SSDs) leads to performance degradation, as existing defragmentation methods are not optimized for SSDs and often require physical data rearrangement, which is inefficient.
Innovation Solution
A data storage device with a flash translation layer that uses a lookaside table to manage logical-to-physical address mappings, allowing for defragmentation without physical data rearrangement, except in response to specific trigger events, thereby optimizing input/output performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If physical data rearrangement is performed to defragment files in SSD, then file-system fragmentation is reduced, but input/output performance deteriorates and processing overhead increases
Solution Approach 1:
The patent creates a copy of the L2P table (lookaside table) to store alternative physical address mappings. When defragmentation is needed, the system updates the lookaside table with new contiguous physical addresses for fragmented files, while the original L2P table remains unchanged. This allows logical defragmentation without physically moving data in the flash memory, thus avoiding I/O performance degradation.
Solution Approach 2:
The lookaside table acts as an intermediary between the host file system and the physical flash memory. It provides a layer of abstraction that allows the system to present a defragmented view to the host while maintaining the original physical data layout in flash memory. This intermediary mechanism enables defragmentation without the harmful side effects of physical data rearrangement in SSDs.
2Stability of the object's composition
If physical data rearrangement is performed for defragmentation, then file continuity is improved, but data access time increases due to additional processing
Solution Approach 1:
Instead of physically moving data to create contiguous layouts, the patent copies the relevant L2P entries to the lookaside table with updated physical addresses that provide contiguous access patterns. This copying approach achieves the effect of data continuity at the logical level without the time-consuming physical data movement operations.
3Stability of the object's composition
If traditional defragmentation methods are used in SSD, then file organization is improved, but device complexity increases due to additional physical operations
Solution Approach 1:
The lookaside table serves as an intermediary structure that simplifies the defragmentation process. Rather than implementing complex physical data movement and reorganization operations, the system simply updates the lookaside table with new address mappings. This reduces device complexity by replacing complex physical operations with simple table updates.
4Productivity
If logical address mappings are updated without physical rearrangement, then I/O performance is maintained, but end-to-end data protection becomes more challenging
Solution Approach 1:
When updating the lookaside table with new physical addresses, the system simultaneously updates the corresponding logical-address tags in the copied L2P entries. This ensures that end-to-end data protection mechanisms, which rely on matching logical addresses with physical data, continue to function correctly even though physical data rearrangement is avoided.
Data Source
AI summary
A data storage device having a flash translation layer configured to handle file-system defragmentation in a manner that avoids, reduces, and/or optimizes physical data movement in flash memory. In an example embodiment, the memory controller maintains in a volatile memory thereof a lookaside table that supplants pertinent portions of the logical-to-physical table. Entries of the lookaside table are configured to track source and destination addresses of the host defragmentation requests and are logically linked to the corresponding entries of the logical-to-physical table such that end-to-end data protection including the use of logical-address tags to the user data can be supported by logical means and without physical data rearrangement in the flash memory. In some embodiments, physical data rearrangement corresponding to the file-system defragmentation is performed in the flash memory in response to certain trigger events, which can improve the input/output performance of the data-storage device.