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    SubjectRe: [PATCH 1b/7] dlm: core locking
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    On Thursday 28 April 2005 12:45, Lars Marowsky-Bree wrote:
    > On 2005-04-28T09:39:22, Daniel McNeil <daniel@osdl.org> wrote:
    > > Since a DLM is a distributed lock manager, its usage is entirely for
    > > locking some shared resource (might not be storage, might be shared
    > > state, shared data, etc). If the DLM can grant a lock, but not
    > > guarantee that other nodes (including the ones that have been kicked
    > > out of the cluster membership) do not have a conflicting DLM lock, then
    > > any applications that depend on the DLM for protection/coordination
    > > be in trouble. Doesn't the GFS code depend on the DLM not being
    > > recovered until after fencing of dead nodes?
    >
    > It makes a whole lot of sense to combine a DLM with (appropriate)
    > fencing so that the shared resources are protected. I understood David's
    > comment to rather imply that fencing is assumed to happen outside the
    > DLM's world in a different component; ie more of a comment on sane
    > modularization instead of sane real-world configuration.

    But just because fencing is supposed to happen in an external component,
    we can't wave our hands at it and skip the analysis. We _must_ identify the
    fencing assumptions and trace the fencing paths with respect to every
    recovery algorithm in every cluster component, including the dlm.

    I suspect that when we do get around to properly scrutinizing fencing
    requirements of specific recovery algorithms, we will find that the fencing
    system currently on offer for gfs needs a little work.

    Regards,

    Daniel
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