DRAM-less SSD HMB Cache Management via Local Log Shadowing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Host memory buffer (HMB) cache management in DRAM-less SSDs is challenging due to transient nature of HMB, which is not always available, especially when the link between the data storage device and the host device is inactive, leading to increased device complexity and potential firmware issues.
Innovation Solution
Implementing an HMB log within the HMB controller that mirrors the HMB, allowing access to delta data even when the link is inactive by writing data to a cache and updating the HMB log to indicate delta data presence, enabling data accessibility both when the link is active and inactive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If HMB is used for caching metadata to reduce controller cost, then controller cost is reduced, but HMB availability becomes problematic when link is inactive
Solution Approach 1:
The patent applies preliminary action by maintaining an HMB log in the controller that proactively records delta data (changes) before the link becomes inactive. This allows the controller to have cached metadata available locally even when the link to host memory is down, resolving the availability issue while keeping controller cost low.
Solution Approach 2:
The HMB log acts as an intermediary between the controller and host memory buffer. It stores delta data that bridges the gap when the direct HMB link is inactive, allowing the controller to access recent metadata changes without needing continuous link availability to host memory.
2Adaptability or versatility
If multiple flows are maintained for active and idle power modes, then power management flexibility is improved, but device complexity increases
Solution Approach 1:
The HMB log serves multiple functions: it acts as a cache for delta data during active mode, provides data access during idle mode, and enables seamless transitions between power states. This single structure handles both active and idle power management scenarios, eliminating the need for separate complex flows.
Solution Approach 2:
The system changes operational parameters based on link status rather than maintaining separate flows. When the link is active, the controller accesses HMB directly; when inactive, it uses the HMB log. This parameter-based approach simplifies firmware logic compared to maintaining multiple independent operational flows.
3Productivity
If HMB is accessed during host idle time for maintenance operations, then maintenance efficiency is improved, but host power consumption increases
Solution Approach 1:
The HMB log proactively captures and stores delta data during active periods before maintenance operations are needed. This preliminary recording of changes allows maintenance to proceed using the log data during host idle time without requiring the host memory to remain powered on, thus maintaining efficiency while reducing power consumption.
Data Source
AI summary
The present disclosure generally relates to host memory buffer (HMB) cache management in DRAM-less SSDs. 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.