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    SubjectRe: [patch] document flash/RAID dangers
    >>>> ---
    >>>> There are storage devices that high highly undesirable properties
    >>>> when they are disconnected or suffer power failures while writes are
    >>>> in progress; such devices include flash devices and MD RAID 4/5/6
    >>>> arrays. These devices have the property of potentially
    >>>> corrupting blocks being written at the time of the power failure, and
    >>>> worse yet, amplifying the region where blocks are corrupted such that
    >>>> additional sectors are also damaged during the power failure.
    >>>
    >>> I would strike the entire mention of MD devices since it is your
    >>> assertion, not a proven fact. You will cause more data loss from common
    >>
    >> That actually is a fact. That's how MD RAID 5 is designed. And btw
    >> those are originaly Ted's words.
    >
    > Ted did not design MD RAID5.

    So what? He clearly knows how it works.

    Instead of arguing he's wrong, will you simply label everything as
    unproven?

    >>> events (single sector errors, complete drive failure) by steering people
    >>> away from more reliable storage configurations because of a really rare
    >>> edge case (power failure during split write to two raid members while
    >>> doing a RAID rebuild).
    >>
    >> I'm not sure what's rare about power failures. Unlike single sector
    >> errors, my machine actually has a button that produces exactly that
    >> event. Running degraded raid5 arrays for extended periods may be
    >> slightly unusual configuration, but I suspect people should just do
    >> that for testing. (And from the discussion, people seem to think that
    >> degraded raid5 is equivalent to raid0).
    >
    > Power failures after a full drive failure with a split write during a rebuild?

    Look, I don't need full drive failure for this to happen. I can just
    remove one disk from array. I don't need power failure, I can just
    press the power button. I don't even need to rebuild anything, I can
    just write to degraded array.

    Given that all events are under my control, statistics make little
    sense here.
    Pavel

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


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