Reverse Directory Footer Management in SSD Garbage Collection
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Solution Overview
Problem
The management of metadata in non-volatile memory, particularly in solid-state drives (SSDs), is challenged when using non-standard garbage collection units (GCUs) with fewer than the standard number of semiconductor dies, leading to wasted space and complexity in locating and using reverse directory footers.
Innovation Solution
A method where a reverse directory manager circuit generates entries for each user data block, accumulating them in a buffer until a complete footer data structure is formed, which is then inserted into the write stream, allowing for straightforward detection and writing to the GCU, even with non-standard configurations, and additional data structures like ending footers facilitate footer location within the GCU.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If reverse directory footers are written at fixed physical locations in standard GCUs, then footer detection is simplified, but non-standard GCUs with fewer dies cause wasted space and complexity
Solution Approach 1:
Instead of writing footers at fixed physical locations and having detectors search for them, the patent inverts the approach by having footers write themselves at deterministic relative locations within the data stream. The footer insertion logic is embedded in the write path, allowing footers to automatically position themselves relative to the data they describe, eliminating the need for separate detection mechanisms and accommodating non-standard GCU configurations.
Solution Approach 2:
The footer insertion mechanism serves itself by being integrated into the data write path. When data is written to the GCU, the corresponding footer is automatically inserted at the appropriate relative location within the same write stream. This self-service approach eliminates the need for separate footer writing and detection operations, simplifying the system while maintaining adaptability to different GCU configurations.
2Reliability
If footers are inserted into every write stream, then metadata completeness is improved, but write stream complexity increases
Solution Approach 1:
The patent merges the footer insertion operation with the existing data write stream processing. Instead of treating footer insertion as a separate complex operation, it is combined with the regular data write path, allowing both data and metadata to be written together in a unified stream. This merging reduces overall system complexity while ensuring metadata completeness.
Solution Approach 2:
The write stream structure is designed to universally handle both data and footer insertion through a single integrated path. The same write mechanism that handles user data also automatically inserts the corresponding reverse directory footers at appropriate relative locations. This multi-functional approach simplifies the write stream structure by eliminating the need for separate data and metadata write paths.
Data Source
AI summary
Apparatus and method for managing metadata in a data storage device such as a solid-state drive (SSD). In some embodiments, a write stream is formed of user data blocks to be sequentially written to a non-volatile memory (NVM). An entry of a reverse directory footer is generated for each user data block in the write stream to describe a physical address in the NVM at which the corresponding user data block is to be stored. The entries are accumulated in a buffer memory until the total count of entries reaches a predetermined threshold and a complete footer data structure is formed. The complete footer data structure is thereafter inserted into the write stream for writing, with the data blocks, to the NVM. The complete footer data structure has an overall size that corresponds to an overall size of each of the user data blocks.