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, wherein the plurality of versions of the data item include a plurality of older versions of the data item, each older version being associated with a different time based on storage of that older version of the data item;
entering a degraded state on the distributed storage system, wherein the degraded state has a degree of degradation based on the version of the data item that is used during processing in the degraded state; 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.
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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, wherein the plurality of versions of the data item include a plurality of older versions of the data item, each older version being associated with a different time based on storage of that older version of the data item; entering a degraded state on the distributed storage system, wherein the degraded state has a degree of degradation based on the version of the data item that is used during processing in the degraded state; 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)
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12. 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, wherein the processor provides data for use by an output device to provide an indication to a user or a client that the processing of the data item in the degraded state is based on one of the older versions of the data item. - View Dependent Claims (13, 14, 18, 19, 20)
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15. 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 and a plurality of older versions of the data item with metadata on a different storage server, the metadata is used to maintain consistent degraded views of the distributed storage system during processing in a degraded state, wherein the degraded state has a degree of degradation based on the version of the data item that is used during processing in the degraded state. - View Dependent Claims (16, 17)
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Specification