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File system snapshots over fully provisioned volume file in direct mode

  • US 9,256,614 B1
  • Filed: 06/28/2013
  • Issued: 02/09/2016
  • Est. Priority Date: 06/28/2013
  • Status: Active Grant
First Claim
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1. A data storage system for use by a file system consumer according to a file system interface, comprising:

  • one or more physical, non-transitory, nonvolatile storage devices; and

    a processing subsystem executing software to form a multi-level stack of functional components including a lower-deck file system and an upper-deck file system, the upper-deck file system providing the file system interface to the file system consumer, the lower-deck file system presenting a volume file from which storage is provided to the upper-deck file system, units of storage of the storage devices being reserved to the upper-deck file system, the volume file being fully provisioned based on the reserved units of storage so that an out-of-space condition is not presented to the upper-deck file system, the reserved units of storage being added dynamically to the volume file to increase its allocated size in response to demand from the upper-deck file system, the lower-deck file system initially operating in a direct mode in which a block address of a data block in the lower-deck file system is obtained by a predetermined calculation from a corresponding block address of a data block in the volume file,wherein the volume file is a primary volume file, and one or more snapshots of the primary volume file are created and stored in respective snapshot volume files of the lower-deck file system, each snapshot being a respective point-in-time copy of the primary volume file, and wherein the lower-deck file system transitions into a mapped mode of operation upon creation of the snapshots, the mapped mode including use of generally arbitrary mappings of respective block addresses of data blocks of the primary volume file and snapshot volume files to obtain corresponding block addresses of the data blocks in the lower-deck file system.

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