Re: ext4 features (checksums)

[Bill Davidsen]

Helge Hafting wrote:
> 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.
Current RAID code supports having a bitmap of dirty stripes, and can 
just sync those during recovery. I'm sure Neil could explain it better, 
but this is available without worrying about fs type. Now. Today.

--
Bill Davidsen <davidsen@xxxxxxx>
  Obscure bug of 2004: BASH BUFFER OVERFLOW - if bash is being run by a
normal user and is setuid root, with the "vi" line edit mode selected,
and the character set is "big5," an off-by-one errors occurs during
wildcard (glob) expansion.

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