Re: How to remount btrfs without compression?

[Lubos Kolouch <lubos.kolouch@gmail.com>]

dima, Wed, 09 Nov 2011 10:01:13 +0900:

> On 11/09/2011 12:12 AM, Chris Mason wrote:
>> On Tue, Nov 08, 2011 at 10:01:51AM -0500, Chris Mason wrote:
>>> On Tue, Nov 08, 2011 at 11:00:42AM +0900, dima wrote:
>>>> On 11/08/2011 10:54 AM, Eric Griffith wrote:
>>>>> On 11/7/2011 8:52 PM, Fajar A. Nugraha wrote:
>>>>>> On Tue, Nov 8, 2011 at 8:06 AM, Eric
>>>>>> Griffith<egriffith92@gmail.com> wrote:
>>>>>>> Edit your fstab, remove the compress flag, reboot. Tell btrfs to
>>>>>>> rebalance the system,
>>>>>>> reboot again. And I -THINK- that'll decompress all the files
>>>>>>
>>>>>> I think the original question was how to force uncompressed mode,
>>>>>> whether specific to a file or to a whole filesystem, without having
>>>>>> to reboot :)
>>>>>>
>>>>>> AFAIK there's no way to do that.
>>>>>>
>>>>>>
>>>>> Whoops! Misunderstood the question haha. Yeah, as far as
>>>>> decompressing just a single file; from what I've read, thats
>>>>> impossible.
>>>>
>>>>
>>>> Eric, Fajar,
>>>> Thanks. Understood.
>>>>
>>>> Yes, it is possible to remove the compress flag from fstab, reboot
>>>> and even do not do any defragmentation/rebalancing - just re-save the
>>>> file and it will be saved uncompressed. This works. But only with
>>>> reboot...
>>>
>>> chattr -c on the file should work (followed by defrag or rewriting the
>>> file).  I just retested and it seems to be broken right now.
>>>
>>> I'll track it down.
>>
>> Ok, I had forgotten.  chattr -c clears the compression flag bug doesn't
>> set the no compress flag.  We looks like we need to patch chattr for
>> this.
>>
>> -chris
>>
>>
> 
> 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.
> 
> ~dima

Sorry for possibly OT question - when I have historical btrfs system
mounted with zlib compression,

can I remount it with lzo ? What will happen? Will the COW be broken
and the files taking duplicate space? Or will the Universe explode and
be replaced with something even more bizzare?

Thank you 

Lubos