Messages in this thread | | | From | Andreas Dilger <> | Date | Fri, 17 Aug 2001 11:25:25 -0600 | Subject | Re: ext2 not NULLing deleted files? |
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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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