Gracefully degradable versioned storage systems
First Claim
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1. A method for use in a distributed storage system, the method comprising:
- maintaining a plurality of versions of a data item including a latest version and an older version;
entering a degraded state on the distributed storage system; and
if the latest version of the data item is unavailable in the degraded state, then using the older version of the data item during processing in the degraded state.
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Abstract
Multiple versions of data on different sets of machines allow a system to degrade gracefully even when experiencing excessive failures. When excessive failures cause the latest versions to be unavailable, the system becomes degraded, but still offers an old version if available. A most recent coherent set of the available older versions is found and provided. The degree of degradation increases gradually as the system experiences more and more failures. Graceful degradation is desirably complementary to fault tolerance.
57 Citations
20 Claims
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1. A method for use in a distributed storage system, the method comprising:
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maintaining a plurality of versions of a data item including a latest version and an older version; entering a degraded state on the distributed storage system; and if the latest version of the data item is unavailable in the degraded state, then using the older version of the data item during processing in the degraded state. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A distributed storage system comprising:
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a versioned data store comprising a plurality of data storage devices across which a plurality of versions of a data item are stored, including a latest version and older versions; and a processor that determines whether to enter a degraded state, and during processing in the degraded state, determines whether to use the latest version of the data item or one of the older versions of the data item. - View Dependent Claims (15, 16, 17)
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18. A method for use in a distributed storage system, the method comprising:
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receiving an update to a version of a data item that is stored on a storage server; creating a new version of the data item; and storing the new version of the data item with metadata on a different storage server, the metadata for use to maintain consistent degraded views of the distributed storage system during processing in the degraded state. - View Dependent Claims (19, 20)
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Specification