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Reconstruction of dense tree volume metadata state across crash recovery

  • US 9,836,355 B2
  • Filed: 09/22/2016
  • Issued: 12/05/2017
  • Est. Priority Date: 09/10/2014
  • Status: Active Grant
First Claim
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1. A method comprising:

  • storing a first upper level of a multi-level dense tree structure and a second upper level of the multi-level dense tree structure in a memory of a storage system coupled to one or more solid state devices (SSDs), wherein each level of the multi-level dense tree structure includes volume metadata entries for storing volume metadata, the volume metadata entries of the first upper level associated with a first generation identifier (ID), the volume metadata entries of the second upper level associated with a second generation ID;

    recording the volume metadata entries in an append log stored on the SSDs, each recorded volume metadata entry tagged with one of the first generation ID associated with the first upper level and the second generation ID associated with the second upper level;

    triggering a merge operation to merge the volume metadata entries of the first upper level of the multi-level dense tree structure with the volume metadata entries of a next lower level of the multi-level dense tree structure when the first upper level is full, the volume metadata entries of the merged levels recorded to the SSDs; and

    recovering from a crash of the storage system during the merge operation by reading merged metadata entries from the SSDs into the memory and replaying entries of the append log to recreate the first upper level and the second upper level of the multi-level dense tree structure, such that the first upper level and second upper level are consistent with restarting the merge operation.

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