Re: btrfs is using 25% more disk than it should

[Josef Bacik <jbacik@fb.com>]

On 12/19/2014 02:59 PM, Daniele Testa wrote:
> No, I don't have any snapshots or subvolumes. Only that single file.
>
> The file has both checksums and datacow on it. I will do "chattr +C"
> on the parent dir and re-create the file to make sure all files are
> marked as "nodatacow".
>
> Should I also turn off checksums with the mount-flags if this
> filesystem only contain big VM-files? Or is it not needed if I put +C
> on the parent dir?

Please God don't turn off of checksums.  Checksums are tracked in 
metadata anyway, they won't show up in the data accounting.  Our csums 
are 8 bytes per block, so basic math says you are going to max out at 
604 megabytes for that big of a file.

Please people try to only take advice from people who know what they are 
talking about.  So unless it's from somebody who has commits in 
btrfs/btrfs-progs take their feedback with a grain of salt.  Thanks,

Josef