On 11/10/2011 11:23 AM, dima wrote:
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?
Hi David
I tried the nocow utility. It worked.
First I made sure to re-save the syslinux.cfg file while btrfs was
mounted with lzo to ensure that it is compressed, then I set the NOCOW
flag with your utility. Then I checked fragmentation of the file and
since it was a small one it was not fragmented. So when I ran btrfs fi
defrag syslinux.cfg it did not have any effect and file was not
uncompressed. Then I simply re-saved the file and it got uncompressed
fine since bootloader could read it on reboot.
thanks
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