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 03:26:14PM +0300, Alexander Tomokhov wrote:
> There is an unanswered question at stackexchange:
> http://unix.stackexchange.com/q/303130/41572
> 
> Assume that we don't invoke mount options like nodatacow and nodatasum - operate only at file attributes level, which are controlled with lsattr/chattr. So does setting No_COW on a file (chattr +C) imply disabling data checksumming on it? The same way as mount options behave (nodatacow implies nodatasum)? Moreover may it disable checksumming only for newly written extents and keep for reading existing ones?

   Yes, it does imply disabling checksums.

   If you have extents in the file when +C is set, then the flag is
ignored (even for new extents, as far as I know): you can only
usefully set +C on a file with no extents.

   So, to use +C, you either need to touch the file first, then set +C
on it, then open the file and write to it, or you need to have +C set
on the parent directory.

   Hugo.

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Hugo Mills             | Comic Sans goes into a bar, and the barman says, "We
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