Write Cache Page Descriptor Segmentation for Storage Latency
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Solution Overview
Problem
Current data storage systems face challenges in efficiently managing write operations, particularly in handling write hot data and unreplicated data during asynchronous replication, which can lead to increased latency and reduced storage efficiency.
Innovation Solution
The system employs a method involving a write cache or log that includes a page descriptor (PDESC) tier and a page buffer (PB) tier for initial write operation recording, with selected write data pages being demoted to a physical large block (PLB) pool for longer-term storage, allowing for extended write cache capacity and improved resource utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If write data is stored in page buffers (PBs) of the write cache, then write operation speed is improved, but storage capacity is limited
Solution Approach 1:
The write cache is segmented into multiple pools: page descriptor pool (PDESC), page buffer pool (PB), and physical large block pool (PLB). This segmentation allows different types of data to be stored in different pools optimized for their specific needs, thereby expanding overall storage capacity while maintaining fast write performance for active data.
Solution Approach 2:
The invention extends the write cache by adding a new dimension of storage hierarchy with the PLB pool. Data transitions from PB to PLB represent movement to an extended storage dimension, effectively multiplying the write cache capacity beyond traditional limits while preserving fast write paths.
2Loss of time
If page buffers are allocated for all write operations, then write latency is reduced, but resource utilization efficiency deteriorates
Solution Approach 1:
Different pools are assigned different qualities and purposes: PDESC for metadata, PB for active write data requiring fast access, and PLB for extended storage of less frequently accessed write data. This local quality differentiation ensures that resources are optimized for their specific functions, improving both latency for active data and overall resource utilization efficiency.
Solution Approach 2:
The system dynamically changes parameters such as pool selection, data placement, and demotion thresholds based on workload characteristics. This allows the write cache to adapt to varying demands, maintaining low latency when needed while optimizing resource utilization through intelligent data placement and demotion strategies.
3Reliability
If write hot data and unreplicated data are managed separately, then replication reliability is improved, but system complexity increases
Solution Approach 1:
The unified write cache structure serves multiple functions: it handles write hot data, unreplicated data, and replicated data within the same framework. The same pools and mechanisms are used for different data types, reducing system complexity while maintaining replication reliability through consistent data management policies.
Solution Approach 2:
The system employs feedback mechanisms to track replication status and data hotness, dynamically adjusting data placement and demotion decisions. This feedback-driven approach ensures replication reliability is maintained while avoiding the need for complex separate management systems for different data types.
Data Source
AI summary
In at least one embodiment, processing can include: receiving write operations; persistently recording, in a write cache or log, the write operations using page descriptors (PDESCs) of a PDESC pool and page buffers (PBs) of a PB pool; selecting, in accordance with criteria, write data pages stored in the PB pool for demotion to a physical large block (PLB) pool included in backend non-volatile storage, wherein each write data page selected denotes content written by a corresponding one of the write operations; responsive to the selecting, persistently storing the write data pages of the PB pool in the PLB pool; and updating PDESCs associated with the write data pages to reference corresponding storage locations in the PLB pool rather than in the PB pool.