Date: Wed, 1 Apr 2020 17:47:17 +0100 From: Martin Simmons <martin@lispworks.com> To: mike tancsa <mike@sentex.net> Cc: freebsd-fs@freebsd.org Subject: Re: zfs promote Message-ID: <202004011647.031GlHqa011166@higson.cam.lispworks.com> In-Reply-To: <42019eac-4211-8265-e73e-d3b418b870fe@sentex.net> (message from mike tancsa on Wed, 1 Apr 2020 10:09:55 -0400) References: <c86e4b80-664d-1ebe-7f50-c59b3c78421d@sentex.net> <202004011102.031B2an5008896@higson.cam.lispworks.com> <42019eac-4211-8265-e73e-d3b418b870fe@sentex.net>
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>>>>> On Wed, 1 Apr 2020 10:09:55 -0400, mike tancsa said:
>
> On 4/1/2020 7:02 AM, Martin Simmons wrote:
> >
> > Were you intending to keep both nfs3zroot/cyclenet and nfs3zroot/cyclenetlive?
>
> No, just nfs3zroot/cyclenetlive
OK, that simplifies things.
> > Not quite. Beware this from the documentation:
> >
> > "The clone parent-child dependency relationship is reversed, so that the
> > origin file system becomes a clone of the specified file system."
> >
> > and
> >
> > "The snapshot that was cloned, and any snapshots previous to this snapshot,
> > are now owned by the promoted clone."
> >
> > Therefore doing zfs promote nfs3zroot/cyclenetlive will cause
> > nfs3zroot/cyclenet to become a clone of nfs3zroot/cyclenetlive@clean3. If you
> > then want to destroy nfs3zroot/cyclenetlive@clean3, you will first need to
> > destroy nfs3zroot/cyclenet.
>
> Hmm, I am trying to get my head around this. I should first simulate
> this in a test environment of course. What you wrote however seems
> reversed, but perhaps my perspective is backwards to what is written ?
Yes, promote is a snapshot twister :-)
> ie Originally I did a
>
>
> zfs clone nfs3zroot/cyclenet@clean3 nfs3zroot/cyclenetlive
>
> so I read that as I made a clone called cyclenetlive of the snapshot
> nfs3zroot/cyclenet@clean3 ?
Correct.
I.e. before promote, nfs3zroot/cyclenet and nfs3zroot/cyclenetlive share data
with the @clean3 snapshot of nfs3zroot/cyclenet:
nfs3zroot/cyclenet@clean3
^ ^
| |
| nfs3zroot/cyclenetlive
|
nfs3zroot/cyclenet
> So if promote reverses that, so
> nfs3zroot/cyclenet@clean3 becomes a clone of nfs3zroot/cyclenetlive ?
> so I can then delete nfs3zroot/cyclenet@clean3 ?
No, that is confused, at least in the names of things:
nfs3zroot/cyclenet@clean3 is a snapshot so it cannot itself be a clone.
What happens is that the @clean3 snapshot is transferred from
nfs3zroot/cyclenet to nfs3zroot/cyclenetlive, so it now called
nfs3zroot/cyclenetlive@clean3. ("The snapshot that was cloned, and any
snapshots previous to this snapshot, are now owned by the promoted clone.")
In addition, nfs3zroot/cyclenet ("the origin file system") becomes a clone of
nfs3zroot/cyclenetlive ("the specified file system"), joined at the
transferred @clean3 snapshot.
I.e. after promote, nfs3zroot/cyclenet and nfs3zroot/cyclenetlive share data
with the @clean3 snapshot of nfs3zroot/cyclenetlive:
nfs3zroot/cyclenetlive@clean3
^ ^
| |
| nfs3zroot/cyclenet
|
nfs3zroot/cyclenetlive
That is why you would then need to destroy nfs3zroot/cyclenet before you can
destroy nfs3zroot/cyclenetlive@clean3.
__Martin
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