Re: How to remount btrfs without compression?

[Eric Griffith <egriffith92@gmail.com>]

On 11/7/2011 7:55 PM, dima wrote:
> On 11/07/2011 09:19 PM, Martin Steigerwald wrote:
>> Am Montag, 7. November 2011 schrieb dima:
>>> Hello,
>>
>> Hi Dima,
>>
>>> Is there any possibility to remount a compressed btrfs without any
>>> compression at all?
>>>
>>> Syslinux bootloader does not understand any btrfs compression and
>>> whenever I edit syslinux.cfg on my compressed / subvolume, the file
>>> becomes compressed and thus unreadable by syslinux on the next boot=
=2E
>>>
>>> I tried to remount / without the 'compress' option (and edit
>>> syslinux.cfg in uncompressed state) and while the "mount" command w=
ould
>>> not show compression any more, I can see in the /proc/mounts that
>>> compression is still there and the file still gets compressed after
>>> editing. But there seem to be no mount option like compress=3Dnone =
or
>>> something.
>>>
>>> The only workaround I found is to boot from a live CD mount / witho=
ut
>>> any compression and re-save syslinux.cfg. Then it the file gets
>>> uncompressed.
>>>
>>> Are there any other options except for this workaround to temporari=
ly
>>> remount btrfs without compression?
>>
>> What does lsattr show on the file? Have you tried chattr -c on the
>> file? It
>> might help to do a btrfs filesystem defrag on the file to remove
>> compression, cause I don=C2=B4t think chattr -c itself will uncompre=
ss it.
>
> Hi Martin,
> Thanks for your reply.
> Yes, I did check out lsattr. It shows that no flags are set. Setting
> chattr +c then chattr -c and re-saving file has no effect either.
>
> I also tried to defragment the file itself and the directory where it
> was in without setting -c but it would not have any effect because / =
is
> mounted with compression.
>
>> As far as I understand it is possible to individually set compressio=
n
>> on/off on single files.
>
> Could not find how to turn it off though.
>
> thanks
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Hey Dima, I know if you install a system without the compress flag=20
already done, you can force BTRFS to compress everything post-install b=
y=20
teling it to "rebalance" the filesystem. I'm under Win7 right now so I=20
dont know the exact command. Check btrfs --help for that.

I dont know if it works in reverse, but you can definitely try it. Edit=
=20
your fstab, remove the compress flag, reboot. Tell btrfs to rebalance=20
the system, reboot again. And I -THINK- that'll decompress all the file=
s
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