Re: Does data checksumming remain for files with No_COW file attribute?

[Hugo Mills <hugo@carfax.org.uk>]

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On Sat, Sep 24, 2016 at 05:40:12PM +0500, Roman Mamedov wrote:
> On Sat, 24 Sep 2016 15:26:14 +0300
> Alexander Tomokhov <alexoundos@ya.ru> wrote:
> 
> > does setting No_COW on a file (chattr +C) imply disabling data checksumming on it?
> 
> Yes. IIRC the reasoning was that it's more difficult to track checksums of
> data which is being overwritten in-place (as opposed to CoW).

   It's because you can't update the data and the checksum atomically
-- at some point in the writing process, they must be inconsistent.
This is considered a Bad Thing.

   Hugo.

> > may it disable checksumming only for newly written extents and keep for reading existing ones?
> 
> You can't apply chattr +C to any files of non-zero length, so by definition
> there won't be any pre-existing checksummed extents in that file.
> 
> -- 
> With respect,
> Roman



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