From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miao Xie Subject: Re: can subvolumes be specified as compressed? Date: Thu, 29 Jul 2010 18:04:27 +0800 Message-ID: <4C51522B.8090304@cn.fujitsu.com> References: <4C5139FB.8070504@cn.fujitsu.com> Reply-To: miaox@cn.fujitsu.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linux-btrfs@vger.kernel.org To: Wang Shaoyan Return-path: In-Reply-To: List-ID: 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: >> 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 >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >>> >> >> > > >