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    SubjectRe: [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck)
    Ric Wheeler wrote:
    > Theodore Tso wrote:
    >> On Thu, Jan 17, 2008 at 04:31:48PM -0800, Bryan Henderson wrote:
    >>> But I heard some years ago from a disk drive engineer that that is a
    >>> myth just like the rotational energy thing. I added that to the
    >>> discussion, but admitted that I haven't actually seen a disk drive
    >>> write a partial sector.
    >>
    >> Well, it would be impossible or at least very hard to see that in
    >> practice, right? My understanding is that drives do sector-level
    >> checksums, so if there was a partially written sector, the checksum
    >> would be bogus and the drive would return an error when you tried to
    >> read from it.
    >
    > There is extensive per sector error correction on each sector written.
    > What you would see in this case (or many, many other possible ways
    > drives can corrupt media) is a "media error" on the next read.

    Correct.


    > You would never get back the partially written contents of that sector
    > at the host.

    Correct.


    > Having our tools (fsck especially) be resilient in the face of media
    > errors is really critical. Although I don't think the scenario of a
    > partially written sector is common, media errors in general are common
    > and can develop over time.

    Agreed.

    Jeff





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