Virtual Hard Disk Booting via Layered Storage
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Solution Overview
Problem
Existing technologies face challenges in quickly booting computer systems or virtual machines when local storage is unavailable, as they rely on network-based storage, which is costly, prone to failures, and reduces performance, especially when copying large amounts of data from remote storage.
Innovation Solution
A virtual storage device is maintained as a chain of data structures, with 'far' data stored remotely and 'near' data stored locally, allowing access to near data for reads and writes, and background copying to fill the near data, enabling fast booting and reducing reliance on network storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If data is copied from remote storage to local storage, then boot speed is improved, but network resources are consumed and storage setup becomes more complex
Solution Approach 1:
The storage system is segmented into multiple layers: a remote base layer containing the full disk image and local differencing layers containing only the changes. This segmentation allows the system to boot quickly using local differencing data while maintaining the ability to access the complete disk image remotely, thus improving boot speed without requiring complete local storage copies.
Solution Approach 2:
The patent introduces a new dimension to storage architecture by implementing a hierarchical storage model with remote and local components working together. Instead of choosing between entirely local or entirely remote storage, the system operates across both dimensions simultaneously, using local differencing layers for fast access and remote base layers for complete data storage.
2Loss of time
If network-based storage is used, then boot time is reduced, but network resources are consumed indefinitely and performance is reduced
Solution Approach 1:
The system performs preliminary actions by creating local differencing layers that capture storage changes before they would otherwise require network access. By pre-computing and storing only the differences locally, the system minimizes subsequent network resource consumption while maintaining fast access times for both boot operations and ongoing storage access.
3Speed
If complete local storage copy is made, then access speed is improved, but storage space requirements increase
Solution Approach 1:
Instead of copying the entire disk image locally, the system copies only the differencing data - the changes from the remote base layer. This selective copying approach maintains fast local access speeds for modified data while using minimal local storage space, as differencing data is typically much smaller than the complete disk image.
Data Source
AI summary
Described is a technology by which a virtual hard disk is maintained between a far (e.g., remote) backing store and a near (e.g., local) backing store, which among other advantages facilitates fast booting of a machine coupled to the virtual hard disk. Read requests are serviced from the near backing store (e.g., a differencing layer) when the data is available thereon, or from the far backing store (e.g., a base layer) when not. The near backing store may be configured with a cache layer that corresponds to the base layer and a write differencing layer that stores writes, or a single differencing layer may be used for both caching read data and for storing write data. A background copy operation may be used to fill the cache until the far backing store data is no longer needed.