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

[Phillip Susi <psusi@ubuntu.com>]

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On 12/19/2014 2:59 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?

If you don't want the overhead of those checksums, then yea.  Also I
would question why you are using btrfs to hold only big vm files in
the first place.  You would be better off using lvm thinp volumes
instead of files, though personally I prefer to just use regular lvm
volumes and manually allocate enough space.  It avoids the
fragmentation you get from thin provisioning ( or qcow2 ) at the cost
of a bit of overallocated space and the need to do some manual
resizing to add more if and when it is needed.

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