Re: du accuracy

[Liu Bo <bo.li.liu@oracle.com>]

On Fri, Apr 10, 2015 at 11:25:57AM +1000, Russell Coker wrote:
> I'm copying an image of a 2G microSD card to a BTRFS filesystem.  The SD card 
> is from an Android phone and is almost full of Android packages and photos, 
> there's very little space on the filesystem and what space there is probably 
> isn't filled with zeros.
> 
> # ls -l
> total 888000
> -rw-r--r--. 1 root root 1043529728 Apr 10 11:20 2gsd
> 
> While doing it I run ls commands to see the progress and get output like the 
> above.  Why is the file size according to ls not matching the total used?
> 
> # du -h
> 886M    .
> 
> When I ran du immediately afterwards it also reported that there was less than 
> 1G used.
> 
> # du -h
> 1.2G    .
> # du -h
> 1.2G    .
> # du -h
> 1.1G    .
> # du -h
> 1.1G    .
> # du -h
> 1.1G    .
> # du -h
> 1.2G    .
> # du -h
> 1.2G    .
> 
> Above are some consecutive du runs.  Why does the space used go from 1.2G to 
> 1.1G before going up again?  The file was created by "cat /dev/sde > 2gsd" so 
> it definitely wasn't getting smaller.
> 
> What's going on here?

What's your mount options?  with autodefrag or compression?

Thanks,

-liubo
> 
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