[Nottingham] Copy without copying?

J J jasonirwin73 at gmail.com
Fri Jun 7 14:39:14 UTC 2019

I will answer myself - OverlayFS!

sudo mount -t overlay -o
lowerdir=source,upperdir=scratch/scratch,workdir=scratch/working none target

On Fri, 7 Jun 2019 at 15:12, J J <jasonirwin73 at gmail.com> wrote:

> I have some tests I'd like to run and in order to get them going the first
> thing I can to do is copy a large(ish) folder structure that can be
> read/written by the tests. This copy is then discarded.
> The copying is wasteful in terms of time and disc space, so I'd like to
> avoid having to do that.
> Clearly any changes could be record as a difference, so my question is:
> 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
> I'm pretty sure if we had ZFS or something this would be possible, but
> that's not the case here. Wondering if FUSE or something can be used to
> fake it.
> My current reading suggests the answer is "No", but I thought I'd ask some
> experts.
> J.
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