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

[Alex Xu]

On 12/03/14 03:15 AM, Yuxuan Shui wrote:
> 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
>

While I can't comment too much on the technical aspects, they seem to be
relatively sound.

However, there are some issues with the, er... other aspects, for lack
of better terminology.

1. This is possibly out of scope as a Gentoo project, since ZOL is not
really part of Gentoo. If it's not, then you're out of luck, because ZOL
is not an accepted organization.

2. This is likely too small to be a GSoC project. Perhaps see [0] for a
list of example ideas, if only so you can get a grasp on the size of a
good project.

It does sound like a good idea though, and even if you can't do it as
part of GSoC, you should pursue it anyways.