Flexible Virtual Volume Block Pointer Replacement
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Solution Overview
Problem
The challenge in storage systems is to efficiently transfer and recreate dual vbn hybrid virtual volumes between source and destination aggregates while maintaining data integrity, as the mapping of physical volume block pointers is not preserved, leading to issues during image transfers and snapshot management.
Innovation Solution
A multi-stage technique is employed to invalidate and replace loadable physical volume block numbers with temporary placeholders, allowing the storage system to serve data immediately and eliminate latency by using a deswizzle scanner to compute and replace actual block pointers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If physical volume block pointers are used in dual vbn hybrid virtual volumes, then data integrity is maintained, but image transfer efficiency deteriorates due to mapping preservation issues
Solution Approach 1:
The patent applies preliminary action by pre-computing and storing the mapping between first virtual volume block numbers (vvbns) and second virtual volume block numbers (vvbns) in a container map before image transfer occurs. This pre-established mapping allows the destination system to directly translate block pointers without needing to preserve complex physical volume block pointer relationships, thereby maintaining data integrity while significantly improving image transfer efficiency.
2Loss of time
If actual block pointers are replaced immediately, then data access latency is reduced, but system complexity increases due to multi-stage replacement process
Solution Approach 1:
The patent segments the block pointer replacement process into multiple stages: first, temporary placeholders are inserted in place of actual block pointers; second, the deswizzle scanner gradually replaces these placeholders with actual block pointers in the background. This segmentation allows the system to immediately reduce data access latency by using placeholders, while the complex replacement process occurs asynchronously without blocking operations.
Solution Approach 2:
The patent introduces temporary placeholders as intermediary elements between the original block pointers and the final actual block pointers. These placeholders serve as mediators that allow the system to function immediately with simplified pointers while the background deswizzle scanner gradually replaces them with actual block pointers, balancing latency reduction with manageable complexity.
3Productivity
If temporary placeholders are used instead of actual block pointers, then image transfer speed is improved, but data access requires additional translation steps
Solution Approach 1:
The patent applies preliminary action by pre-computing the vvbn-to-vvbn mappings and storing them in the container map before image transfer. This preliminary preparation enables rapid image transfer using temporary placeholders, while the translation complexity is resolved in advance rather than during data access operations.
Solution Approach 2:
The patent creates a copied mapping structure (container map) that translates between different vvbn spaces. This copying approach allows the system to use simple temporary placeholders during transfer while maintaining the ability to perform accurate translations through the pre-computed container map, improving transfer speed without permanently increasing access complexity.
Data Source
AI summary
A multi-stage technique invalidates and replaces loadable physical volume block numbers (pvbns) stored in indirect blocks of a dual vbn (“flexible”) virtual volume (vvol) of a storage system to enable efficient image transfers and/or fragmentation handling of the flexible vvol. Each loadable pvbn of a pvbn/virtual vbn (vvbn) block pointer pair is converted into a special block pointer having a predefined reserved value that provides a temporary “pvbn_unknown” placeholder until replaced by a real (actual) pvbn. The technique further allows the storage system to serve data from the flexible vvol using the placeholders while the actual pvbns are computed, thereby eliminating latencies associated with completion of actual pvbn replacement for the pvbn_unknown placeholders.