Changed-Block Bitmap Management for Storage Volume Copy Consistency

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Solution Overview

Problem

Existing methods for managing changed-block bitmaps in storage volumes face challenges in maintaining consistency between a copy of a storage volume and its corresponding data structure, especially when storage commands continue to be executed during the creation of the copy, leading to potential performance degradation or infeasibility due to atomicity requirements.

Innovation Solution

The approach involves creating a copy of the data structure and resetting it, then creating a copy of the storage volume while continuing to execute and update the data structure, and finally merging the data structure into the copy using a bit-wise OR operation, ensuring consistency without requiring atomicity between the storage volume and data structure operations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the computing system creates a copy of the storage volume while continuing to execute storage commands and update the data structure, then productivity is improved by avoiding stalls, but reliability deteriorates due to potential inconsistency between the copy and data structure

Engineering Contradiction:

Improvestorage command execution continuityVSAvoidconsistency between volume copy and data structure

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system creates a preliminary copy of the data structure (bitmap) before the storage volume copy is completed. This preliminary bitmap copy is then updated by merging it with the original data structure after the volume copy is finished, ensuring consistency without stalling storage commands during the copy process.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces an intermediary data structure (the bitmap) that mediates between the storage volume and its copy. By operating on the bitmap separately and merging it afterward, the system achieves consistency without requiring atomic operations or stalling storage commands, thus resolving the contradiction between productivity and reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the system requires atomic creation of data structure copy and storage volume copy, then reliability is improved by ensuring consistency, but device complexity increases and productivity decreases

Engineering Contradiction:

Improveconsistency between volume copy and data structureVSAvoidatomicity requirement implementation

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the copy operation into two independent phases: (1) creating a preliminary copy of the data structure without waiting for volume copy completion, and (2) merging the data structures after volume copy is finished. This segmentation eliminates the need for complex atomicity mechanisms while maintaining consistency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system performs preliminary copying of the data structure before the storage volume copy is complete, then applies preliminary updates by merging the original data structure into the copied data structure afterward. This approach avoids the complexity of atomic operations while ensuring consistency.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the system stalls storage commands during data structure copy creation, then reliability is improved by ensuring atomicity, but productivity deteriorates due to command execution interruption

Engineering Contradiction:

Improveatomicity of data structure copyVSAvoidstorage command execution rate

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system creates a preliminary copy of the data structure without stalling storage commands. Storage commands continue to execute and update the original data structure throughout the copy process. The preliminary bitmap copy is then updated by merging it with the original data structure after the volume copy is finished, maintaining both reliability and productivity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent maintains continuous execution of storage commands during the data structure copy process. By using a preliminary bitmap copy that is updated afterward through merging, the system ensures that useful storage operations continue uninterrupted, preserving productivity while achieving consistency through the merge operation.

Inventive Principle:

Principle #20Continuity of useful action

Data Source

PatentUS10929238B2Management of changed-block bitmaps

Publication Date: 2021.02.23 MELLANOX TECHNOLOGIES LTD(IL)

AI summary

An apparatus includes an interface and a processor. The interface is configured to communicate with a computing system in which one or more workloads issue storage commands for execution in a storage volume comprising multiple storage blocks. The computing system continually updates a data structure that tracks which of the storage blocks of the storage volume have changed due to the storage commands. The processor is configured, in response to a request to create a copy of the storage volume, to instruct the computing system to (i) create a copy of the data structure and reset the data structure, (ii) create the copy of the storage volume, while continuing to execute the storage commands and update the data structure, and (iii) after the copy of the storage volume is completed, merge the data structure into the copy of the data structure.