File System Cache Log Entry Mapping for Low Latency
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Solution Overview
Problem
Data storage systems face delays in processing host write requests due to the need for time-consuming mapping operations when caching data, especially when metadata from disk is required, diminishing the cache's effectiveness in providing fast responses.
Innovation Solution
The technique involves creating log entries in both a first and second data log to store data in a cache page and acknowledge the host, allowing for quick caching and acknowledgment of host write requests, with subsequent mapping and flushing to disk performed out of band to maintain high performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If data storage systems perform mapping operations and read metadata from disk prior to storing data in cache, then data can be correctly placed in cache location, but the cache response time increases significantly
Solution Approach 1:
The system performs mapping operations and reads metadata from disk in advance, before actual data write operations occur. By pre-establishing the mapping between cache locations and disk locations, the system eliminates the need to perform these time-consuming operations during the critical data write path, thus reducing cache response time while maintaining placement accuracy.
Solution Approach 2:
The patent separates the data write operation from the mapping operation. The write path is segmented to only handle data placement in cache, while mapping is handled by a separate pre-processing component. This segmentation allows the critical write path to be fast while the non-critical mapping path can be slower and more thorough.
2Reliability
If data storage systems perform two levels of mapping for host-accessible file systems served from internal file systems, then data can be correctly mapped to physical addresses, but the processing delay increases
Solution Approach 1:
The system performs both levels of mapping (host file system to internal file system, and internal file system to physical disk) in advance, before actual data write operations. By pre-computing the complete mapping chain, the system eliminates mapping delays from the critical write path while ensuring accurate address translation through both file system layers.
3Reliability
If data storage systems require metadata from disk to be read before caching data, then cache can store data with proper metadata, but the cache effectiveness is greatly diminished
Solution Approach 1:
Metadata is read from disk and prepared in advance, before data write operations occur. This preliminary metadata preparation ensures that when data arrives at the cache, the corresponding metadata is already available in memory, eliminating disk I/O delays during the critical data caching operation while maintaining metadata accuracy.
Data Source
AI summary
A technique for storing data in a data storage system includes receiving, from a host, a request specifying a set of data to be written to a first file system, the first file system realized as a file within a second file system. A first log entry is created for the set of data in a first data log, which logs data to be written to the first file system, and a second log entry is created for the set of data in a second data log, which logs data to be written to the second file system. The first log entry provides a reference to the second log entry. The technique further includes storing the data in the cache page and acknowledging the host.