Re: How to remount btrfs without compression?

[Dmitry Olenin <dolenin@parallels.com>]

On 11/10/2011 03:57 PM, Lubos Kolouch wrote:
> Dmitry Olenin, Wed, 09 Nov 2011 17:03:39 +0900:
>
>> On 11/09/2011 04:48 PM, Lubos Kolouch wrote:
>>> 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?
>>
>> Hello Lubos If you have a kernel that supports lzo (don't quite remember
>> when it got in), why can't you?
>> Absolutely nothing will happen, and only the new/updated files will be
>> with lzo compression. You can remount on the fly switching b/w the two
>> compression options without any problems.
>
> Hello Dmitry,
>
> By the way, this is interesting question to me - I mounted the filesystem
> with -o compress=lzo, in dmesg showed btrfs: use lzo compression,
>
> but - the lzo module was not loaded (not shown in lsmod - and yes, I have
> it as a module).
>
> When I do modprobe lzo, it shows there.
>
> Isn't it a bit strange? So btrfs is using lzo module that was not loaded?
> (and says so in the dmesg output)?

Hello Lubos
Yes, I was wondering about this too when I started doing lzo.
The lzo module you load most likely has nothing to do with btrfs. This 
is the only explanation. I would think that lzo for btrfs is built into 
kernel. Unfortunately I don't have my .config with me at the moment to 
check it.