[Nottingham] Copy without copying?

VM vadim at mankevich.co.uk
Fri Jun 7 16:13:27 UTC 2019

well, a simple lvm snapshot would work that way, but you'd have to create a new volume group etc. and make sure its size is sufficient for syoring all changed blocks.

On June 7, 2019 3:47:19 PM UTC, J J via Nottingham <nottingham at mailman.lug.org.uk> wrote:
>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
>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
>> > volume" that appear to be like a copy but isn't. The tests can do
>> 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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