zfs discuss - Jan 2010 - Can I use a clone to split a filesystem?

I''ve been reading the zfs man page, but I''m confused about
dependancies.  I have a ZFS filesystem that I wish to split into two
ZFS filesystems at one of the subdirectories.  I understand that I
first need to make a snapshot of the filesystem and then make a clone
of the snapshot, with a different name.  Then, in the clone I can move
everything in that subdirectory up to the top level, and in the
original I can remove that subdirectory.  All of these operations
should be quick, with no copying of data.

I understand also that I won''t be able to destroy the snapshot because
the clone is dependant on it.  Can I just promote the clone and then
destroy the snapshot?  Does that remove all dependancies?

I suppose a simpler case, without the file shuffling, would be to
create a second filesystem as a copy of a first.  All of the examples
of this I''ve seen destroy the first filesystem but don''t
destroy the
snapshot.  I want to do the opposite.  Is this possible?

-- 
-Gary Mills-        -Unix Group-        -Computer and Network Services-

On Fri, Jan 15, 2010 at 02:07:40PM -0600, Gary Mills
wrote:
> I have a ZFS filesystem that I wish to split into two
> ZFS filesystems at one of the subdirectories.  I understand that I
> first need to make a snapshot of the filesystem and then make a clone
> of the snapshot, with a different name.  Then, in the clone I can move
> everything in that subdirectory up to the top level, and in the
> original I can remove that subdirectory.  All of these operations
> should be quick, with no copying of data.
> 
> I understand also that I won''t be able to destroy the snapshot
because
> the clone is dependant on it.  Can I just promote the clone and then
> destroy the snapshot?  Does that remove all dependancies?
No.  A clone and the parent filesystem are always bound together through
that snapshot.  You can''t remove it as long as both filesystems remain
in existence. 
> I suppose a simpler case, without the file shuffling, would be to
> create a second filesystem as a copy of a first.  All of the examples
> of this I''ve seen destroy the first filesystem but don''t
destroy the
> snapshot.  I want to do the opposite.  Is this possible?
Snapshots don''t create copies.  If you want them to be truly
independent, you''d have to create the filesystem and then copy the data
manually.
-- 
Darren