Re: APFS cloning not working across volumes inside same container?
Re: APFS cloning not working across volumes inside same container?
- Subject: Re: APFS cloning not working across volumes inside same container?
- From: Thomas Tempelmann <email@hidden>
- Date: Tue, 07 May 2019 16:52:31 +0200
That makes sense to me.
Thank you for taking the time to explain.
Thomas
On Tue, May 7, 2019 at 4:33 PM Dominic Giampaolo <email@hidden>
wrote:
>
> > I accept that it's currently not possible - but just to help me
> understand this, could you please elaborate:
> >
> > In theory, would it be possible to share a cloned file between two
> volumes? Since they're in the same container, and the space management is
> container-wide, could this be made possible? Or are there technical reason
> why this couldn't work at all (such as that IDs needed to manage this are
> not sharable between volumes)?
> >
> Space management (i.e. is this block allocated or not) is shared. But
> cloning introduces another layer which is a reference count the blocks and
> that is not shared between volumes within a container. Further it's
> complicated by snapshots and the management of the reference counts across
> snapshots and the live view of the file system.
>
> Consider what would happen if you cloned a file between two volumes, took
> a snapshot on both volumes, modified part of the file on one of the volumes
> then deleted it on the other. Managing the reference counting would be a
> nightmare, especially since you'd have to manage locking some new shared
> data structure between two different volumes.
>
> We'll definitely think about it but as always, a compelling use case is
> needed to justify the work. In other words, we can't just do something
> because it would be kinda cool - there has to be a good reason to expend
> the effort required to do it.
>
>
> --dominic
>
>
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