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Waveter
Asked: 2016-06-11 03:00:11 +0800 CST

Locking mechanism on pNFS

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As I know, in parallel NFS, after getting Layout from Meta Data Server, Client communicate directly with the Data Server. I wander what will happen if multi clients read or write to the same region of the Data Server simultaneously. Are there any machanism for locking in pNFS.

linux nfs nfs4

1 Answers

  1. Best Answer

    As per RFC 5661 (nfs 4.1 incl. pnfs)
    https://www.rfc-editor.org/rfc/rfc5661#section-12.5.1

    The requirement of NFSv4.1 that all user access rights MUST be
    obtained through the appropriate OPEN, LOCK, and ACCESS operations is not modified with the existence of layouts. Layouts are provided to
    NFSv4.1 clients, and user access still follows the rules of the
    protocol as if they did not exist. It is a requirement that for a
    client to access a storage device, a layout must be held by the
    client.

    And further down in the same section:

    Note, clients are still required to perform the appropriate OPEN, LOCK, and ACCESS operations as described above. The degree to which it is possible for the client to circumvent these operations and the consequences of doing so must be clearly specified by the individual layout type specifications. In addition, these specifications must be clear about the requirements and non-requirements for the checking performed by the server.

    In the presence of pNFS functionality, mandatory byte-range locks
    MUST behave as they would without pNFS. Therefore, if mandatory file locks and layouts are provided simultaneously, the storage device
    MUST be able to enforce the mandatory byte-range locks. For example, if one client obtains a mandatory byte-range lock and a second client accesses the storage device, the storage device MUST appropriately
    restrict I/O for the range of the mandatory byte-range lock. If the
    storage device is incapable of providing this check in the presence
    of mandatory byte-range locks, then the metadata server MUST NOT
    grant layouts and mandatory byte-range locks simultaneously.

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