Re: How to remount btrfs without compression?

[dima <dolenin@parallels.com>]

On 11/10/2011 09:11 AM, David Sterba wrote:
> On Wed, Nov 09, 2011 at 10:01:13AM +0900, dima wrote:
>> Just for the record - I could find a solution thanks to the btrfs wiki
>> being online again. In Gotchas it says
>>
>> mount -o nodatacow also disables compression
>>
>> and indeed it does. Remounting with this option and re-saving the file
>> makes it uncompressed. However, I could not find how to remount the
>> filesystem afterwards without nodatacow.
>
> I saw this mentioned on irc today (that nodatacow diasables
> compression). There is a way how to turn off compression on a file --
> with help of the NOCOW _file_ attribute, ie. you don't have to remount.
>
> * create the file, compression enabled
> * set NOCOW (with the attached single-purpose nocow.c utility)
> * btrfs fi defrag the_file
>
> Make sure you have enough free space for the uncompressed file size. You
> can compare the extent layout before and after the defrag with
> "filefrag -v" .


Hello David,

Thank you, I will try it out tonight. Is there any way to see if nocow 
attribute was set on a particular file, and is there any way to unset it?

thanks
~dima