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? -- 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
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 > >-- 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
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 <miaox@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
>> --
>> 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
>>
>>
>
>
--
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
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<miaox@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 >>> -- >>> 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 >>> >>> >> >> > > >-- 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
So, is there such a method: in a specified directory, the compression feature is enabled, and the file in this directory will be compressed automatically, while the others don''t enable compression. thanks. 2010/7/29 Wang Shaoyan <stufever@gmail.com>:> 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 <miaox@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 >>> -- >>> 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 >>> >>> >> >> > > > > -- > Wang Shaoyan >-- 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
Hi, > So, is there such a method: in a specified directory, the > compression feature is enabled, and the file in this directory > will be compressed automatically, while the others don''t enable > compression. I don''t think so, but it wouldn''t be difficult -- you''d just set a per-inode flag on whether to compress, and if it''s set on a directory then it''s inherited by the files in that directory. I think the hold up has been that we''ve waited for a *generic* cross-filesystem flag to appear, and it hasn''t (or it has and I didn''t notice). Does anyone have suggestions on how to break the deadlock there? - Chris. -- Chris Ball <cjb@laptop.org> One Laptop Per Child -- 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
I don''t know whether this demand, which specified some subvolumes or directories to be compressed, conflict with the design of btrfs''s compression feature, may be they want to do this thing well, and everyone will enable the compression feature, rather than throw the decision to user to determine which should compress. But now, if we can mount a subvolume and specify some mount options, we should make these options work, rather than ignore. 2010/7/30 Chris Ball <cjb@laptop.org>:> Hi, > > > So, is there such a method: in a specified directory, the > > compression feature is enabled, and the file in this directory > > will be compressed automatically, while the others don''t enable > > compression. > > I don''t think so, but it wouldn''t be difficult -- you''d just set a > per-inode flag on whether to compress, and if it''s set on a directory > then it''s inherited by the files in that directory. > > I think the hold up has been that we''ve waited for a *generic* > cross-filesystem flag to appear, and it hasn''t (or it has and I didn''t > notice). Does anyone have suggestions on how to break the deadlock > there? > > - Chris. > -- > Chris Ball <cjb@laptop.org> > One Laptop Per Child >-- 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
Hi, > I don''t know whether this demand, which specified some subvolumes > or directories to be compressed, conflict with the design of > btrfs''s compression feature, may be they want to do this thing > well, and everyone will enable the compression feature, rather > than throw the decision to user to determine which should > compress. You can''t tell whether you can compress data well until you''ve already spent CPU compressing it, though. Right now we have a useful metric of "if parts of the file fail to compress, bail out on compressing the rest of the file, both now and in the future"; but it''s only a metric. There are cases this fails on, such as a tar archive that starts out with JPEGs and continues with large (compressible) text files. I think the argument that we don''t need to offer user control because we can just do a good job all the time only works if it''s actually true that we can do a good job all the time, and I don''t think that''s true here. So, I still support user control of the per-inode flag. (I agree about the subvol flags; I think being able to set quotas and compression per-subvol is on the roadmap and just not done yet.) -- Chris Ball <cjb@laptop.org> One Laptop Per Child -- 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