[gentoo-dev] GSoC proposal: cp --reflink support for zfs.

[Yuxuan Shui]

Hi,

I would like to implement cp --reflink support for ZFSOnLinux as my GSoC
project.

cp --reflink is used to create a COW copy of a file, so the file will not
take any disk space if it's not modified. This feature is very useful for
cases like storing a lot of almost identical virtual machine images. Also
this is a frequently requested feature for ZoL. [1][2][3]

Currently only btrfs support this feature, so my goal it to bring it to ZoL
as well.

I think the only way to do it (without changing too many parts of ZoL) is
to use the deduplication feature of zfs. A COW copy could be done by create
a new entry in ddt for the old file, and create a new file which points to
the ddt entry.

Please let me know if this proposal makes sense, and if that's the right
way to do it.

Thanks.

[1]:
https://groups.google.com/a/zfsonlinux.org/forum/#!topic/zfs-discuss/mvGB7QEpt3w
[2]: https://github.com/zfsonlinux/zfs/issues/405
[3]: https://github.com/zfsonlinux/zfs/issues/1063
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Regards
Yuxuan Shui