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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This archive was generated by hypermail 2b29 : Thu Aug 23 2001 - 21:00:24 EST