On Thu, 29 Jul 2010 16:55:03 +0800, Wang Shaoyan wrote:
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.
Sorry! I made a mistake.
According to the implement of the btrfs, after we mount a btrfs filesystem
(include subvol), if we mount the same filesystem again or its subvol, the
kernel doesn't allocate a new super_block object, and use the super_block
object that allocated and initiated at the first mount. So the feature is also
the same as the filesystem mounted first.
Thanks
Miao
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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