Disk Drive Cache Flush via Track Limit Segmentation
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Solution Overview
Problem
Existing disk drives face delays in processing host commands due to the time required to flush write data from the volatile semiconductor memory to the disk, especially when data needs to be written to multiple tracks, which can extend processing times and impact performance.
Innovation Solution
Implementing a method to flush write data from the volatile semiconductor memory to the disk in batches, limiting the number of tracks flushed to a predetermined maximum, thereby reducing the delay in processing host commands during the flush operation, and using a formula to determine an optimal flush limit based on time constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If write data is flushed to multiple tracks on the disk, then the amount of data written to disk increases, but the time required to complete the flush operation increases
Solution Approach 1:
The patent segments the flush operation into multiple passes, each handling a limited number of tracks. The controller flushes data to a predetermined maximum number of tracks in one pass, then performs additional passes for remaining data. This segmentation reduces the time impact of each individual flush operation while still achieving complete data persistence across multiple tracks.
Solution Approach 2:
The patent implements partial action by flushing only a subset of cached data (limited to a predetermined number of tracks) in each flush operation rather than flushing all cached data. This allows the system to make progress on data persistence without committing to completing the entire flush operation, thereby reducing the time penalty for each flush while maintaining data integrity through subsequent passes or flush commands.
2Reliability
If the flush operation is completed fully before processing host commands, then data integrity is ensured, but the delay in processing host commands increases
Solution Approach 1:
The patent segments the flush operation to allow host command processing to occur after a limited number of tracks are flushed rather than waiting for complete cache flush. This segmentation enables the system to maintain data integrity for flushed tracks while improving productivity by allowing host commands to be processed for tracks that have been flushed, with remaining cache data being flushed in subsequent passes.
Solution Approach 2:
The patent applies partial action by performing a partial flush of cached data to a predetermined maximum number of tracks before allowing host command processing to proceed. This ensures data integrity for the flushed portion while avoiding the full time penalty of completing the entire flush operation, thereby improving host command processing speed without completely sacrificing reliability.
3Productivity
If write-back caching is used to improve performance, then the disk drive can immediately return ready status, but the flush operation time is deferred and can impact subsequent performance
Solution Approach 1:
The patent segments the deferred flush operation into multiple smaller flush passes, each handling a limited number of tracks. This segmentation reduces the time impact of each flush operation while maintaining the write-back caching benefit of immediate ready status response to host commands. The segmented approach allows the system to manage flush time more predictably without sacrificing the performance advantage of write-back caching.
Data Source
AI summary
A disk drive having a disk, a head actuated over the disk, a volatile semiconductor memory (VSM), a command queue, and control circuitry operable to receive a plurality of write commands from a host, store the plurality of write commands in the command queue, store write data for the plurality of write commands in the VSM, and flush, from the VSM to the disk, a portion of the write data corresponding to a predetermined number of tracks.