A prerequisite is: when first mounted file system, not specify '-o
compress' options, only on mount subvolume
Below is my test:
# mkfs.btrfs /dev/sda8
# mount /dev/sda8 btrfs
# df
Used: 56k
# btrfs subvolume create mysubvolume
# mkdir some_dir_in_root
# mount -o compress,subvol=mysubvolume /dev/sda8 some_dir_in_root
# cd some_dir_in_root
# dd if=/dev/zero of=bigfile count=2048 //create a all-0 file of 1M byte
# df
Used:1088k
we can find it is not compressed at all.
Another test:if we mount subvolume with "-o compress" first, then we
mount /dev/sda8 without "-o compress", and create a test file in
somewhere not in subvolume, we can find the file is compressed too.
2010/7/29 Miao Xie <mi...@cn.fujitsu.com>:
> On Thu, 29 Jul 2010 15:50:28 +0800, Wang Shaoyan wrote:
>>
>> Hi.
>> I want a subvolume in root to be compressed, I try to do this:
>> # mkfs.btrfs /dev/sda8
>> # mount /dev/sda8 /home/usr/btrfs
>> # cd /home/usr/btrfs
>> # btrfs subvolume create mysubvolume
>> # mount -o compress,subvol=mysubvolume /dev/sda8 some_dir_in_root
>> but when I create a file in some_dir_in_root, the file isn't
>> compressed at all. why? How can I specify some subvolumes to be
>> compressed, and the others Not to be compressed in a single btrfs?
>
> The method that you said is right, by this way, I can create a compressed
> file
> on the specified subvolume.
>
> I think your file has been compressed or is hard to be compressed, so
> you found it isn't compressed at all. Just like we use a zip tool to
> compress
> a compressed file, we will find the file isn't compressed at all.
>
> Thanks
> Miao
>
>>
>> --
>> Wang Shaoyan
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>>
>
>
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Wang Shaoyan
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