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    SubjectRe: raid is dangerous but that's secret (was Re: [patch] ext2/3: document conditions when reliable operation is possible)
    On 08/27/2009 06:13 PM, Pavel Machek wrote:
    >
    >>>> Repeat experiment until you get up to something like google scale or the
    >>>> other papers on failures in national labs in the US and then we can have an
    >>>> informed discussion.
    >>>>
    >>> On google scale anvil lightning can fry your machine out of a clear sky.
    >>>
    >>> However, there are still a few non-enterprise users out there, and knowing
    >>> that specific usage patterns don't behave like they expect might be useful to
    >>> them.
    >>
    >> You are missing the broader point of both papers. They (and people like
    >> me when back at EMC) look at large numbers of machines and try to fix
    >> what actually breaks when run in the real world and causes data loss.
    >> The motherboards, S-ATA controllers, disk types are the same class of
    >> parts that I have in my desktop box today.
    > ...
    >> These errors happen extremely commonly and are what RAID deals with well.
    >>
    >> What does not happen commonly is that during the RAID rebuild (kicked
    >> off only after a drive is kicked out), you push the power button or have
    >> a second failure (power outage).
    >>
    >> We will have more users loose data if they decide to use ext2 instead of
    >> ext3 and use only single disk storage.
    >
    > So your argument basically is
    >
    > 'our abs brakes are broken, but lets not tell anyone; our car is still
    > safer than a horse'.
    >
    > and
    >
    > 'while we know our abs brakes are broken, they are not major factor in
    > accidents, so lets not tell anyone'.
    >
    > Sorry, but I'd expect slightly higher moral standards. If we can
    > document it in a way that's non-scary, and does not push people to
    > single disks (horses), please go ahead; but you have to mention that
    > md raid breaks journalling assumptions (our abs brakes really are
    > broken).
    > Pavel
    >


    You continue to ignore the technical facts that everyone (both MD and ext3)
    people put in front of you.

    If you have a specific bug in MD code, please propose a patch.

    Ric



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