SSD Write Ordering via Sequence Tags
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Solution Overview
Problem
Storage devices face challenges in maintaining write coherency and consistency due to out-of-order processing of I/O commands, which can lead to incorrect data retrieval and illegal overwrites, especially when multiple applications access shared data and background operations interfere with processing queues.
Innovation Solution
Implementing a sequence tag generator logic to assign sequence tags to I/O commands, a command handler logic to process commands in order based on these tags, and a notification logic to coalesce and return completion notices in the correct order, ensuring that I/O commands are processed and notified in the sequence they were issued.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If I/O commands are processed in parallel across multiple internal channels to improve throughput, then productivity increases, but write coherency and data consistency deteriorate due to out-of-order execution
Solution Approach 1:
The patent applies preliminary action by assigning sequence tags to I/O commands before they are dispatched to multiple internal channels. This pre-tagging allows the storage device to track and reorder command completions according to their original sequence, ensuring write coherency is maintained even when commands are executed in parallel across different channels.
Solution Approach 2:
The patent implements feedback mechanisms where the storage device monitors the completion status of I/O commands across multiple channels and uses sequence tags to determine the correct order for notifying the host. This feedback loop ensures that despite parallel processing, the host receives completions in the correct sequential order, maintaining data consistency.
2Adaptability or versatility
If multiple applications are allowed to access shared data simultaneously to improve versatility, then adaptability increases, but data consistency deteriorates due to conflicting write operations
Solution Approach 1:
The patent applies preliminary action by assigning unique sequence tags to each I/O command from multiple applications before processing. This pre-tagging enables the storage device to maintain a global sequence order across all applications, ensuring that write operations are executed and completed in a consistent order regardless of which application initiated them.
Solution Approach 2:
The sequence tag mechanism acts as an intermediary that mediates between multiple applications accessing shared data. By using sequence tags to order and track commands from different applications, the storage device ensures that data consistency is maintained while allowing simultaneous access from multiple sources.
3Reliability
If background operations like garbage collection are performed to improve storage media health, then reliability improves, but I/O command processing speed deteriorates due to channel occupation
Solution Approach 1:
The patent applies segmentation by dividing I/O command processing across multiple independent internal channels, each with its own processing queue. This allows background operations like garbage collection to occur on specific channels without completely blocking I/O processing, as other channels can continue handling commands simultaneously.
Solution Approach 2:
The patent ensures continuity of useful action by allowing I/O command processing to continue on available channels even when some channels are occupied by background operations. The sequence tag mechanism tracks all commands across channels, ensuring that processing remains continuous and efficient while maintaining the ability to perform necessary background maintenance tasks.
Data Source
AI summary
Disclosed are systems and methods by which a storage device may process and return I/O commands to a host in the order in which the host provided the commands, thereby reducing host overhead, including but not limited to the following: receiving a first I/O command and a second I/O command, the first I/O command and the second I/O command being assigned a sequence tag, issuing the first I/O command and the second I/O command to one or more storage channels based on their respective sequence tags, collecting a command completion notice of the first I/O command or the second I/O command when the first I/O command or the second I/O command has been respectively completed; and issuing a command completion notification to a host based on the sequence tag of the associated completed first I/O command or the second I/O command.