[Nottingham] Copy without copying?

[J J]

Thanks for the tips. Overlay is deffo an improvement as it will only take a
copy of a file if there is a change but it's still a full copy of the
entire file.
I am wondering if there's a way that XFS, ZFS or whatever can do something
even deeper and maintain partial/block differences or something.

On Fri, 7 Jun 2019 at 16:25, Andy Smith via Nottingham <
nottingham at mailman.lug.org.uk> wrote:

> Hello,
>
> On Fri, Jun 07, 2019 at 03:12:21PM +0100, J J via Nottingham wrote:
> > With Ext4, is there some magic way I can create and ad hoc "differencing
> > volume" that appear to be like a copy but isn't. The tests can do what
> they
> > like and that the whole thing gets chucked.
> > i.e. avoiding the copy operation
>
> You already found overlayfs. Another possible answer is btrfs or
> xfs, which support copy on write.
>
> By using either of those you can do cp --reflink=always … and it
> will do a copy that only adds a reference to the source, not an
> actual copy of the data. This uses no additional space. If you alter
> one of the copies then the link is broken.
>
> And of course btrfs also has writeable snapshots.
>
> Cheers,
> Andy
>
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