SMR Drive Write Command Handling During Refresh
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Shingled magnetic recording (SMR) hard disk drives (HDDs) face inefficiencies in handling refresh operations, leading to significant write amplification and latency due to the need to rewrite entire bands when updating data, and host-managed SMR HDDs experience high-latency events during refresh operations, delaying write commands.
Innovation Solution
The HDD suspends refresh operations upon receiving a write command for a band undergoing refresh, stores the write data in nonvolatile memory, and resumes the refresh operation after data storage, using nonvolatile memory such as spare SMR bands or protected solid-state memory to manage write commands efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire SMR band is rewritten to update a small amount of data, then data integrity is maintained, but write amplification increases significantly
Solution Approach 1:
The patent segments the SMR band into multiple independent segments that can be updated individually. Instead of rewriting the entire band to update a small portion of data, the system identifies and updates only the specific segment containing the modified data, thereby maintaining data integrity while significantly reducing write amplification.
Solution Approach 2:
The patent performs preliminary actions by pre-positioning data in a cache buffer before the refresh operation completes. When data needs to be updated during a refresh operation, the system has already prepared the updated data in memory, allowing for efficient insertion into the appropriate segment without requiring a complete band rewrite.
2Reliability
If the entire SMR band is rewritten to update data, then data accuracy is preserved, but the time required for the operation increases
Solution Approach 1:
By dividing the SMR band into manageable segments, the system can perform updates on individual segments rather than the entire band. This segmentation enables parallel processing of different segments and reduces the overall operation time while maintaining data accuracy through systematic verification of each segment.
Solution Approach 2:
The system performs preliminary data preparation and validation before the actual write operation. Data is pre-processed and validated in memory, and the necessary metadata is prepared in advance, which significantly reduces the time required for the actual band update operation while ensuring data accuracy.
3Reliability
If write commands are suspended during refresh operations, then data consistency is maintained, but write latency increases drastically
Solution Approach 1:
The system performs preliminary actions by caching write commands and their associated data in memory before the refresh operation completes. This preliminary buffering allows the system to quickly apply multiple write commands once the refresh operation finishes, rather than suspending each individual write command until refresh completion, thereby maintaining data consistency while reducing overall write latency.
Solution Approach 2:
The system maintains continuity of useful action by keeping the write command processing pipeline active even during refresh operations. Instead of completely suspending write operations, the system continues to accept and buffer write commands, validate their integrity, and prepare them for execution, ensuring that the useful work of processing write commands continues without interruption while maintaining data consistency.
Data Source
AI summary
Write commands in a shingled magnetic recording (SMR) drive are efficiently executed when a write command and associated write data are received by an SMR HDD from a host while the target SMR band for storing the write data is undergoing a refresh operation. In response to the write command, the HDD suspends the refresh operation, stores the write data in nonvolatile memory, and informs the host that the write command has been completed. After the write data are stored in nonvolatile memory, the HDD resumes the refresh operation, and the remaining unrefreshed data in the target SMR band are refreshed by being rewritten to the spare SMR band. The nonvolatile memory can include the spare SMR band in some instances, the target SMR band in some instances, and in both the spare SMR band and the target SMR band in some instances.