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    SubjectRe: [patch] ext2/3: document conditions when reliable operation is possible
    On Tue, 25 Aug 2009, Ric Wheeler wrote:

    > On 08/25/2009 07:26 PM, Pavel Machek wrote:
    >>
    >>>>> Basically, any file system (Linux, windows, OSX, etc) that writes into
    >>>>> the page cache will lose data when you hot unplug its storage. End of
    >>>>> story, don't do it!
    >>>>
    >>>> No, not ext3 on SATA disk with barriers on and proper use of
    >>>> fsync(). I actually tested that.
    >>>>
    >>>> Yes, I should be able to hotunplug SATA drives and expect the data
    >>>> that was fsync-ed to be there.
    >>>
    >>> You can and will lose data (even after fsync) with any type of storage at
    >>> some rate. What you are missing here is that data loss needs to be
    >>> measured in hard numbers - say percentage of installed boxes that have
    >>> config X that lose data.
    >>
    >> I'm talking "by design" here.
    >>
    >> I will lose data even on SATA drive that is properly powered on if I
    >> wait 5 years.
    >>
    >
    > You are dead wrong.
    >
    > For RAID5 arrays, you assume that you have a hard failure and a power outage
    > before you can rebuild the RAID (order of hours at full tilt).

    and that the power outage causes a corrupted write.

    >>> I can promise you that hot unplugging and replugging a S-ATA drive will
    >>> also lose you data if you are actively writing to it (ext2, 3, whatever).
    >>
    >> I can promise you that running S-ATA drive will also lose you data,
    >> even if you are not actively writing to it. Just wait 10 years; so
    >> what is your point?
    >
    > I lost a s-ata drive 24 hours after installing it in a new box. If I had MD5
    > RAID5, I would not have lost any.

    me to, in fact just after I copied data from a raid array to it so that I
    could rebuild the raid array differently :-(

    David Lang


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