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    SubjectRe: ext2 not NULLing deleted files?
    On Aug 17, 2001  18:32 +0200, Marc SCHAEFER wrote:
    > Special care, as far as I understand it, must be taken when allocating
    > fs data blocks. The following sequence must be followed:
    >
    > 1. reserve them
    > 2. clear them
    > 3. mark them as allocated.
    >
    > if 2 is too expensive, maybe it's sufficient to mark them as dirty
    > and zero them in memory. But what happens if the system crashes, with
    > the metadata to the disk (block allocated), but the data block not
    > yet filled/zeroed ?

    Ext2 and ext3 both do this already (with caveats). Since ext2 doesn't
    impose write ordering constraints, there is not a hard guarantee that
    the data block makes it to disk before the metadata is updated. If
    you run ext3 in data=ordered or data=journal mode, then you do have
    such a guarantee.

    If you run in data=writeback mode, you basically have the same
    situation as ext2 (data may be written before or after the metadata).
    This is the same as the _current_ reiserfs code, but there are
    apparently patches available which allow data=ordered mode also.

    Cheers, Andreas
    --
    Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto,
    \ would they cancel out, leaving him still hungry?"
    http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert

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