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    Subjectfsck more often when powerfail is detected (was Re: wishful thinking about atomic, multi-sector or full MD stripe width, writes in storage)
    Hi!

    > > Yes, but ext3 was designed to handle the partial write (according to
    > > tytso).
    >
    > I'm not sure what made you think that I said that. In practice things
    > usually work out, as a conseuqence of the fact that ext3 uses physical
    > block journaling, but it's not perfect, becase...

    Ok; so the journalling actually is not reliable on many machines --
    not even disk drive manufacturers guarantee full block writes AFAICT.

    Maybe there's time to reviwe the patch to increase mount count by >1
    when journal is replayed, to do fsck more often when powerfails are
    present?


    > > > Also, when you enable the write cache (MD or not) you are buffering
    > > > multiple MB's of data that can go away on power loss. Far greater (10x)
    > > > the exposure that the partial RAID rewrite case worries about.
    > >
    > > Yes, that's what barriers are for. Except that they are not there on
    > > MD0/MD5/MD6. They actually work on local sata drives...
    >
    > Yes, but ext3 does not enable barriers by default (the patch has been
    > submitted but akpm has balked because he doesn't like the performance
    > degredation and doesn't believe that Chris Mason's "workload of doom"
    > is a common case). Note though that it is possible for dirty blocks
    > to remain in the track buffer for *minutes* without being written to
    > spinning rust platters without a barrier.

    So we do wrong thing by default. Another reason to do fsck more often
    when powerfails are present?
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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