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    SubjectRe: hunt for 2.6.37 dm-crypt+ext4 corruption? (was: Re: dm-crypt barrier support is effective)
    On Tue, Dec 7, 2010 at 2:02 PM, Chris Mason <chris.mason@oracle.com> wrote:
    > Excerpts from Jon Nelson's message of 2010-12-07 14:34:40 -0500:
    >> On Tue, Dec 7, 2010 at 12:52 PM, Chris Mason <chris.mason@oracle.com> wrote:
    >> >> postgresql errors. Typically, header corruption but from the limited
    >> >> visibility I've had into this via strace, what I see is zeroed pages
    >> >> where there shouldn't be.
    >> >
    >> > This sounds a lot like a bug higher up than dm-crypt.  Zeros tend to
    >> > come from some piece of code explicitly filling a page with zeros, and
    >> > that often happens in the corner cases for O_DIRECT and a few other
    >> > places in the filesystem.
    >> >
    >> > Have you tried triggering this with a regular block device?
    >>
    >> I just tried the whole set of tests, but with /dev/sdb directly (as
    >> ext4) without any crypt-y bits.
    >> It takes more iterations but out of 6 tests I had one failure: same
    >> type of thing, 'invalid page header in block ....'.
    >>
    >> I can't guarantee that it is a full-page of zeroes, just what I saw
    >> from the (limited) stracing I did.
    >
    > Fantastic. Now for our usual suspects:
    >
    > 1) Is postgres using O_DIRECT?  If yes, please turn it off

    According to strace, O_DIRECT didn't show up once during the test.

    > 2) Is postgres allocating sparse files?  If yes, please have it fully
    > allocate the file instead.

    That's a tough one. I don't think postgresql does that, but I'm not an
    expert here.

    > 3) Is postgres using preallocation (fallocate)?  If yes, please have it
    > fully allocate the file instead

    As far as strace is concerned, postgreql is not using fallocate in
    this version.

    --
    Jon
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