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    SubjectRe: [PATCH 3/3] Add timeout feature
    On Sun 2008-07-13 13:15:43, jim owens wrote:
    > Pavel Machek wrote:
    >
    >>> This means ONLY SOME metadata (or no metadata) is flushed and
    >>> then all metadata updates are stopped. User/kernel writes
    >>> to already allocated file pages WILL go to a frozen disk.
    >>
    >> That's the difference here. They do write file data, and thus avoid
    >> mmap()-writes problem.
    >>
    >> ...and they _still_ provide auto-thaw.
    >> Pavel
    >
    > One of the hardest things to make people understand is that
    > stopping file data writes in the filesystem during a freeze
    > is not just dangerous, it is also __worthless__ unless you
    > have a complete "user environment freeze" mechanism.

    Eh?

    > And unless each independent component has a freeze and they
    > can all be coordinated, the data in the pipeline is never
    > stable enough to say "if you stop all writes to disk and
    > take a snapshot, this is the same as an orderly shutdown,
    > backup, restore, and startup".

    If you also freeze data writes, at least snapshot is not worse than
    _unexpected_ shutdown.

    And apps should already be ready for unexpected shutdowns (using fsync
    etc).

    Pavel

    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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