Host Memory Buffer Cache Management for NVMe Storage
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Solution Overview
Problem
Host memory buffer (HMB) cache management is hindered by power management guidelines that restrict link power and discourage HMB usage when the host device is idle, leading to increased device complexity and potential firmware issues due to the need for multiple operational flows.
Innovation Solution
Implementing an HMB log within the HMB controller in the data storage device to store deltas since the last copying or link inactivity, allowing access to HMB data even when the link is inactive by mirroring the HMB cache and using a cache management engine to redirect transactions and maintain data accessibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the link power is restricted and HMB usage is discouraged during host idle time to reduce host power consumption, then host power consumption is reduced, but the data storage device loses access to HMB data when the link is inactive
Solution Approach 1:
The patent maintains a local cache in the data storage device that is pre-populated with HMB data before link inactivity occurs. This preliminary caching ensures that data is already available locally when the link becomes inactive, eliminating the need to access HMB during idle periods while maintaining data accessibility.
Solution Approach 2:
The patent introduces a local cache as an intermediary between the data storage device and the host memory buffer. This cache mediates data access by storing copies of HMB data locally, allowing the device to access data independently of HMB availability when the link is inactive, thus resolving the contradiction between power savings and data accessibility.
2Reliability
If multiple flows are implemented to support both active power with HMB access and limited HMB usage during idle periods, then data accessibility is maintained, but device complexity and firmware synchronization challenges increase
Solution Approach 1:
The patent merges the data access paths by implementing a unified cache management system that handles both active and idle states through a single firmware logic flow. The local cache serves as a unified data source that works seamlessly in both link active and inactive states, eliminating the need for separate firmware handling for different operational flows and reducing overall system complexity.
Data Source
AI summary
The present disclosure generally relates to host memory buffer (HMB) cache management. HMB is transient memory and may not always be available. For example, when the link between the data storage device and the host device is not active, the data storage device can't access the HMB. Placing an HMB log in the HMB controller that is disposed in the data storage device provides access to data that would otherwise be inaccessible in the HMB. The HMB log contains any deltas that have occurred since either the last copying to an HMB cache in the memory device or any delta that have occurred since the link became inactive. The HMB cache mirrors the HMB. In so doing, the data of the HMB is available to the data storage device not only when the link is active, but also when the link is not active.