Re: ext4 features (checksums)

[Helge Hafting]

On Tue, Jul 04, 2006 at 01:19:11PM +0200, Krzysztof Halasa wrote:
> Neil Brown <neilb@xxxxxxx> writes:
> 
> > With checksums - the filesystem is in a better position to:
> >  - be selective about what is checksummed - no point checksumming
> >    blocks that aren't part of any file.  Some blocks (highlevel
> >    metadata) might always be checksummed, while other blocks
> >    (regular data) might not if a 'fast' option was chosen.
> 
> The same applies to RAID - for example, why "synchronise" unused area?
> 
Indeed.  RAID usually avoid checksumming unused area, it sums on write
and you don't write "unused" stuff.  

Not syncing unused area is possible, if there was a way for raid resync
to ask the fs what blocks are not in use.  I.e. get the
free block list in disk block order.  Then raid resync could skip those.

Helge Hafting
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