Zoned Namespace Storage Ordering Through Sequence Numbers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The NVMe specification's Relaxed Ordering mechanism can cause zone write commands in NVMe devices implementing the Zoned Namespaces (ZNS) specification to be executed out of order due to issues like command fetch, data transfer, controller-to-firmware APIs, and multi-core processing, which disrupts the sequential advancement of the write pointer in non-volatile memory.
Innovation Solution
A zoned namespaces storage device with a processor configured to execute zone write commands in the order specified by zone write sequence numbers included in zone descriptors, ensuring that commands are executed in the original order by comparing them to the sequence numbers and managing the submission queue accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Relaxed Ordering mechanism is used in NVMe specification, then I/O communication efficiency is improved, but zone write command order is disrupted
Solution Approach 1:
The system performs preliminary actions by capturing the original order of zone write commands through submission queue entries and zone write sequence numbers before execution. This allows the controller to reference the intended sequence during the relaxed ordering processing, ensuring commands are executed in the correct order despite reordering optimizations.
Solution Approach 2:
The system implements feedback mechanisms where the controller monitors and tracks zone write sequence numbers, comparing them against the original order recorded in submission queue entries. This feedback loop enables the controller to detect and correct ordering discrepancies, maintaining reliability while allowing relaxed ordering for improved efficiency.
2Productivity
If zone write commands are processed by multiple cores, then processing throughput is improved, but command execution order is disrupted
Solution Approach 1:
The system segments the command processing by assigning unique zone write sequence numbers to each command and organizing them in submission queue entries. This segmentation allows multiple cores to process commands independently while maintaining individual command ordering through the sequence number tracking mechanism.
Solution Approach 2:
The submission queue entry acts as an intermediary structure that mediates between multiple core processing and maintains command order. It contains the zone write sequence number and original order information, serving as a reference that coordinates execution across multiple cores while preserving the required sequential order.
3Speed
If submission queue entries are fetched from host memory, then command retrieval speed is improved, but order of commands is scrambled
Solution Approach 1:
The system performs preliminary ordering by recording the original sequence of commands in submission queue entries before they are fetched from host memory. This preliminary order information is preserved and used during processing to restore the correct sequence, allowing fast retrieval while maintaining order through the pre-recorded sequence numbers.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A zoned namespace, ZNS, storage computing device includes a processor, and non-volatile memory comprising a plurality of zones including a given zone. The processor is configured to execute a zone writing program to receive zone write commands, and responsive to receiving the zone write commands, execute the zone write commands on the given zone of the non-volatile memory of the storage computing device in an order specified by zone write sequence numbers included in a zone descriptor for the given zone.