SSD Write Scheduling for Mixed Read-Write Workloads
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Solution Overview
Problem
Conventional input-output scheduling schemes for SSDs fail to optimize performance for mixed read-write workloads, resulting in lower bandwidth compared to write-only and read-only workloads.
Innovation Solution
A write scheduling scheme that accumulates write requests in a DRAM buffer for a period of time (approximately 10-20 ms) and issues them in bursts, rather than immediately, to enhance read performance while maintaining write bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If write commands are issued immediately upon receiving requests, then write bandwidth is maintained, but read performance deteriorates
Solution Approach 1:
The patent applies preliminary action by accumulating write requests in a buffer before issuing them to the SSD. Instead of immediately writing each request as it arrives, the system collects multiple write requests over a short time window (e.g., 10-20 ms) and then issues them in a batch. This preliminary accumulation allows the system to optimize the timing and grouping of write operations, reducing the impact on read performance while maintaining overall write bandwidth.
Solution Approach 2:
The patent implements periodic action by using a time-based scheduling mechanism that accumulates write requests for fixed time intervals. The IO scheduler collects write requests during specific time windows (e.g., 10-20 ms periods) and then issues them in bursts. This periodic accumulation and issuance pattern creates a rhythm that allows read operations to proceed between write bursts, thereby improving read bandwidth while still achieving high write throughput through the accumulated batches.
2Productivity
If write commands are randomly distributed over time, then write operations are handled promptly, but read-write mixed workload performance deteriorates
Solution Approach 1:
The patent transforms the random distribution of write commands into a periodic pattern. By accumulating write requests for fixed time intervals (e.g., 10-20 ms) and then issuing them in batches, the system creates a predictable rhythm of write operations. This periodic scheduling improves mixed workload performance by creating regular intervals where read operations can execute without interference from scattered write commands, while the batching mechanism maintains high write throughput.
Solution Approach 2:
The patent uses preliminary action by pre-collecting write requests in a buffer before issuing them to the SSD. This accumulation phase allows the scheduler to group multiple write operations together and issue them in optimized batches rather than handling them individually and randomly. The preliminary buffering and batching approach simplifies the scheduling logic while improving overall mixed workload productivity by reducing the frequency and impact of write interruptions.
Data Source
AI summary
Described is a write scheduling scheme for a SSD that significantly increases read performance, in certain embodiments by about 50% compared to a conventional standard write scheduling schemes, for mixed read-write workloads while maintaining the write bandwidth.