Btrfs devel - Feb 2014 - Meaning of "no_csum" field when scrubbing with -R option

Hello everyone,

I have a question: What exactly does the value for "no_csum" mean when
doing a scrub with the -R option? Example output:


 > sudo btrfs scrub start -BR /

scrub done for ...
   ...
   csum_errors: 0
   verify_errors: 0
   no_csum: 70517
   csum_discards: 87381
   super_errors: 0
   ...


In the btrfs header, I found the following comment for the "no_csum" 
field of the btrfs_scrub_progress struct:


"# of 4k data block for which no csum is present, probably the result of 
data written with nodatasum"


So my question is, why does scrub show a high (i.e. non-zero) value for 
no_csum? I never enabled nodatasum or a similar option.

Best regards
Sebastian
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