Nonvolatile Memory Die Segmentation for Read-Write Contention
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Solution Overview
Problem
In data center servers, the use of SSDs based on NAND flash technology leads to increased read latency due to access contention between read and write operations, degrading I/O performance when a read request is issued during an ongoing write operation, as existing methods either isolate storage regions too much or concentrate data writing, leading to reduced user capacity and shortened SSD lifespan.
Innovation Solution
A memory system that classifies nonvolatile memory dies into physical sets, allowing only one set to handle write operations while others are in read-only mode, and rotates these modes among physical sets to prevent read-on-write-die contention and distribute wear evenly across multiple physical sets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If read requests are allowed on nonvolatile memory dies during write operations, then user capacity and storage utilization are improved, but read latency increases and I/O performance degrades due to access contention
Solution Approach 1:
The patent segments nonvolatile memory dies into multiple groups, where each group is dedicated to either read operations or write operations at any given time. This segmentation allows the system to prevent read-on-write contention by isolating read and write operations into separate memory groups, thereby resolving the contradiction between storage utilization and read latency.
Solution Approach 2:
The patent implements dynamic group switching where memory groups can transition between read-mode and write-mode. The controller dynamically selects which group performs reads and which performs writes based on operation demands, allowing the system to adapt to varying workloads while preventing simultaneous read-write access to the same memory group, thus maintaining low latency while preserving storage utilization.
2Productivity
If write operations are concentrated on fewer memory dies, then write efficiency is improved, but wear on individual dies increases and SSD lifespan is shortened
Solution Approach 1:
The patent divides memory dies into multiple groups that can be independently utilized for write operations. By segmenting the write workload across multiple groups rather than concentrating it on a single group, the system maintains write efficiency while distributing wear more evenly across all dies, thereby extending SSD lifespan.
Solution Approach 2:
The patent implements periodic switching between read-mode and write-mode for different memory groups. Over time, each group undergoes cycles of being dedicated to writes and then to reads, which periodically redistributes the wear burden across all memory groups. This periodic action ensures that no single group bears the full write wear load continuously, thus improving reliability while maintaining productivity.
3Loss of time
If storage regions are isolated to prevent access contention, then read latency is reduced, but user capacity and storage flexibility are reduced
Solution Approach 1:
The patent employs dynamic group assignment where memory groups are not permanently isolated but are dynamically assigned to read or write modes based on real-time workload demands. This dynamic approach maintains the isolation benefits for preventing contention during operations while allowing the system to flexibly reconfigure group assignments, thereby preserving storage flexibility and user capacity.
Solution Approach 2:
The patent makes memory groups universal by allowing them to serve both read and write functions at different times. Each memory group can be configured for reads or writes depending on the operational phase, enabling the same physical resources to fulfill multiple functional roles. This multi-functionality resolves the contradiction by maintaining isolation during operations (reducing latency) while allowing flexible reconfiguration (preserving adaptability).
Data Source
AI summary
According to one embodiment, a memory system includes a nonvolatile memory including a plurality of nonvolatile memory dies, and a controller. The controller classifies the nonvolatile memory dies into a plurality of physical sets such that each of the nonvolatile memory dies belongs to only one physical set. The controller creates a plurality of storage regions which share each of the physical sets and each of which spans the physical sets. The controller sets one of the physical sets to a first mode for permitting a write operation and a read operation, and sets each of the other physical sets to a second mode for permitting a read operation and inhibiting a write operation.