Write Cache Bit Reset for SSD Read Latency Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The management of map structures in data storage devices, such as SSDs, leads to processing bottlenecks due to the need for accurate and efficient retrieval of data, which can be exacerbated by large and frequently updated map entries, increasing latency and resource requirements.
Innovation Solution
A write cache with a forward map that uses a write cache bit value to indicate the residency of data blocks in the cache, allowing for efficient data retrieval by directly accessing the write cache for resident data and the NVM for non-resident data, reducing unnecessary cache searches and maintaining a manageable map structure size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the write cache bit value is not reset after data is jettisoned from cache, then the cache search may incorrectly find non-resident data, but resetting the bit value increases processing overhead and latency
Solution Approach 1:
The forward map entry is updated with the new physical address and the write cache bit is reset to the second value (indicating data is not in cache) before the data is actually jettisoned from the write cache. This preliminary action ensures that when a read command arrives, the system immediately knows the data is not in cache without needing to perform a search, thereby eliminating the time penalty that would otherwise be incurred by searching for non-resident data.
2Measurement precision
If the forward map stores detailed physical addresses for all data blocks, then data retrieval accuracy is improved, but the map structure size and processing complexity increase
Solution Approach 1:
The forward map entry is segmented into distinct components: a physical address field storing the location of data in NVM, and a write cache bit field indicating whether a copy exists in the write cache. This segmentation allows the system to maintain only essential information in the forward map while using the write cache bit as a quick indicator to avoid unnecessary cache searches, thereby reducing overall system complexity.
3Reliability
If the system searches the write cache for every read command, then accurate data retrieval is ensured, but read latency increases due to unnecessary searches
Solution Approach 1:
The write cache bit is set to the first value (indicating data is in cache) when data is written to the write cache, and this bit is checked before executing read commands. This preliminary action allows the system to determine in advance whether a cache search is necessary, avoiding unnecessary searches for non-resident data and reducing read latency while maintaining retrieval accuracy.
Solution Approach 2:
The write cache bit acts as an intermediary indicator between the forward map and the write cache. Instead of directly searching the write cache for every read command, the system first checks this intermediate bit to determine whether the search is necessary, thereby optimizing the read path while ensuring data accuracy.
Data Source
AI summary
Method and apparatus for managing data buffers in a data storage device. In some embodiments, a write manager circuit stores user data blocks in a write cache pending transfer to a non-volatile memory (NVM). The write manager circuit sets a write cache bit value in a forward map describing the NVM to a first value upon storage of the user data blocks in the write cache, and subsequently sets the write cache bit value to a second value upon transfer of the user data blocks to the NVM. A read manager circuit accesses the write cache bit value in response to a read command for the user data blocks. The read manager circuit searches the write cache for the user data blocks responsive to the first value, and retrieves the requested user data blocks from the NVM without searching the write cache responsive to the second value.