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Distributed file system and method

  • US 8,041,735 B1
  • Filed: 11/01/2002
  • Issued: 10/18/2011
  • Est. Priority Date: 11/01/2002
  • Status: Active Grant
First Claim
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1. A method for using a plurality of cluster nodes, each of which has access to a plurality of logical storage volumes, to provide access by clients, in communication with the nodes, to data on the volumes, wherein each volume is restricted to be owned by a single node, wherein only the owner of a volume has permission to write to the volume, the method comprising:

  • storing, by a first node, a file system object in a first volume owned by the first node; and

    creating, in the first node and in a second node, a logical link between the first volume and a second volume owned by the second node, said logical link referring to the file system object in the first volume, wherein the process of creating a logical link between the first volume and second volume includes creating a logical identifier in a directory of the second volume that symbolically identifies the file system object which is referenced by the logical link and creating in a relocation directory of the first volume a hard link to the file system object and creating in the first volume a unique association between the hard link and the logical identifier from the second volume with respect to the file system object, wherein the logical link is represented by the hard link, the logical identifier, and the unique association between the hard link and the logical identifier forms; and

    wherein the hard link increases a reference count associated with the file system object in the first volume independent of the disposition of the logical identifier in the second volume such that the first volume is self-contained while allowing the file system object to be accessed symbolically from the second volume using the logical identifier without a physical cross-volume link;

    a physical namespace invisible to the clients of the plurality of nodes, the physical namespace implemented through the plurality of volumes, each volume having an internal hierarchy that connects file system objects through hard links including the hard link in the relocation directory of the first volume; and

    a logical namespace visible to the clients of the plurality of nodes that spans the entire file system across volumes and is made of file system objects connected via hard links and logical links such that the difference between hard links and logical links is hidden from the clients.

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