Virtual Disk Synchronization via Modified Block Tracking
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Solution Overview
Problem
Maintaining synchronized copies of a virtual disk across multiple physical machines is challenging, as updates to one copy are not reflected in other copies, requiring inefficient data copying and manual synchronization.
Innovation Solution
A virtualization layer maintains records of modified file system blocks during access sessions and synchronizes only relevant, unmodified blocks between copies of a virtual disk, ensuring that updated blocks are copied only when in use, thereby avoiding unnecessary data transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all file system blocks are copied during synchronization, then synchronization completeness is improved, but data transfer volume increases
Solution Approach 1:
The patent segments the file system blocks into two categories: modified blocks and unmodified blocks. By maintaining separate records of modified blocks and comparing them against the destination copy's block status, the system transfers only the necessary modified blocks rather than all blocks, thus reducing data transfer volume while maintaining synchronization completeness.
Solution Approach 2:
The patent applies partial action by transferring only a subset of blocks (specifically, the modified blocks that need synchronization) rather than performing a complete copy of all file system blocks. This selective transfer approach reduces unnecessary data movement while ensuring that all required updates are applied.
2Reliability
If synchronization is performed frequently, then data consistency is improved, but system performance deteriorates
Solution Approach 1:
The patent implements periodic action by performing synchronization only when modified blocks are detected, rather than at fixed time intervals or continuously. The virtualization layer tracks modified blocks and triggers synchronization events only when necessary, reducing the frequency of full synchronization operations while maintaining data consistency.
Solution Approach 2:
The patent uses selective copying of only the modified blocks to the destination copy, rather than copying the entire virtual disk. This reduces the time and resources required for each synchronization operation, thereby improving system performance during synchronization events while maintaining data consistency.
3Productivity
If modified blocks are tracked and selectively copied, then data transfer efficiency is improved, but synchronization complexity increases
Solution Approach 1:
The patent introduces an intermediary mechanism in the form of a modification record or bitmap that tracks which blocks have been modified. This intermediary data structure simplifies the synchronization process by providing a clear indication of which blocks need to be transferred, reducing the complexity of determining synchronization needs compared to comparing entire disk images.
Data Source
AI summary
In order to synchronize copies of a virtual disk, a virtualization layer maintains a first record of file system blocks of a first copy of the virtual disk that are modified during an access session by a virtual machine using the first copy of the virtual disk. The file system blocks correspond to a file system of the virtual disk. During an attempt to synchronize the first copy with a second copy of the virtual disk, (i) a second record of file system blocks that are currently used by the file system is obtained from the guest operating system, and (ii) file system blocks in the first copy of the virtual disk that are present in both the first record and the second record are copied into the second copy of the virtual disk.