Network Boot Cache Consistency During Virtual Disk Rollback
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Solution Overview
Problem
In conventional network boot systems, rolling back a virtual disk leads to inconsistency between the rolled-back disk and cache data on terminals, resulting in increased network access and decreased boot speeds when multiple terminals are booted simultaneously.
Innovation Solution
A network boot system with a read cache mechanism that stores generation management data on client terminals, allowing the system to identify modified regions of the virtual disk and maintain cache data consistency by using this data to reduce network access and optimize cache utilization during rollbacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the virtual disk is rolled back to a past revision, then the system can return to a previous state, but consistency between the rolled back virtual disk and the cache data on the terminal side cannot be maintained and the cache data cannot be utilized
Solution Approach 1:
The patent applies preliminary action by storing generation management data in advance on both the server and terminal sides. This data records which regions of the virtual disk have been modified in each revision. When a rollback occurs, the terminal uses this pre-stored generation management data to identify which cache data regions remain valid and can be reused, rather than discarding all cache data. This preliminary preparation enables efficient rollback while maintaining cache utilization.
2Reliability
If all cache data is discarded and the rolled back virtual disk is re-cached, then consistency is restored, but when a large number of terminals are booted all at once, a number of network accesses to the server from the terminals is large and loads are concentrated on the server so that boot speeds of the terminals decrease
Solution Approach 1:
The patent applies local quality by treating different regions of cache data differently based on their validity status. Instead of uniformly discarding all cache data during a rollback, the system uses generation management data to identify which specific cache regions remain valid (unchanged since the rollback point) and which regions need to be updated. This selective approach allows valid cache regions to be reused locally, reducing network access requirements and improving boot speeds while maintaining consistency where needed.
3Speed
If a read cache mechanism is provided to cache virtual disk data on terminal, then network access to the server is reduced and boot speeds are improved, but when the virtual disk is revised, all cache data must be discarded and re-cached, causing network load to increase
Solution Approach 1:
The patent applies parameter changes by introducing generation management data that tracks the revision state of different virtual disk regions. This parameter (generation/revision information) allows the system to determine which cache data remains valid after a revision. By changing from a binary cache validity model (all valid or all invalid) to a granular model (region-specific validity based on generation matching), the system reduces network access volume while maintaining boot performance.
Data Source
AI summary
In a network boot system 100, a network boot server and a terminal 20a are connected through a network 30, the network boot server providing a disk image as a virtual disk 22a that includes an operating system operating on the terminal, the terminal 20a being provided with a physical storage device 21a. The operating system is provided with a read cache mechanism that stores data read from the server as cache data in the storage device. Further, the read cache mechanism is provided with generation management data for generation-managing a transition of revision that represents revise information of the virtual disk. The generation management data is divided for each transition of the revision and stored in the server and a copy of at least one division of the divided generation management data is also stored in the storage device.