Matt,
This is really cool! One thing that I can think of that would be nice to
have is the ability to 'promote' and 'sync'. In other words, just prior
to promoting the clone, bring any files that are newer on the original
parent up-to-date on the clone. I suspect you could utilize zfs diffs
(CR# 6370738) to provide this functionality and apply the diffs.
BTW, would there have to be any special handling for the top level
parent filesystem associated with the pool?
Thanks,
George
Matthew Ahrens wrote:
FYI folks, I have implemented "clone promotion", also known as "clone
swap" or "clone pivot", as described in this bug report:
6276916 support for "clone swap"
Look for it in an upcoming release...
Here is a copy of PSARC case which is currently under review.
1. Introduction
1.1. Project/Component Working Name:
ZFS Clone Promotion
1.2. Name of Document Author/Supplier:
Author: Matt Ahrens
1.3 Date of This Document:
06 May, 2006
4. Technical Description
ZFS provides the ability to create read-only snapshots of any filesystem,
and to create writeable clones of any snapshot. Suppose that F is a
filesystem, S is a snapshot of F, and C is a clone of S. Topologically,
F and C are peers: that is, S is a common origin point from which F and C
diverge. F and C differ only in how their space is accounted and where
they appear in the namespace.
After using a clone to explore some alternate reality (e.g. to test a patch),
it's often desirable to 'promote' the clone to 'main' filesystem status --
that is, to swap F and C in the namespace. This is what 'zfs promote' does.
Here are man page changes:
in the SYNOPSIS section (after 'zfs clone'):
zfs promote <clone filesystem>
in the DESCRIPTION - Clones section (only last paragraph is added):
Clones
A clone is a writable volume or file system whose initial
contents are the same as another dataset. As with snapshots,
creating a clone is nearly instantaneous, and initially con-
sumes no additional space.
Clones can only be created from a snapshot. When a snapshot
is cloned, it creates an implicit dependency between the
parent and child. Even though the clone is created somewhere
else in the dataset hierarchy, the original snapshot cannot
be destroyed as long as a clone exists. The "origin" pro-
perty exposes this dependency, and the destroy command lists
any such dependencies, if they exist.
The clone parent-child dependency relationship can be reversed by
using the _promote_ subcommand. This causes the "origin"
filesystem to become a clone of the specified filesystem, which
makes it possible to destroy the filesystem that the clone was
created from.
in the SUBCOMMANDS section (after 'zfs clone'):
zfs promote <clone filesystem>
Promotes a clone filesystem to no longer be dependent on its
"origin" snapshot. This makes it possible to destroy the
filesystem that the clone was created from. The dependency
relationship is reversed, so that the "origin" filesystem
becomes a clone of the specified filesystem.
The snaphot that was cloned, and any snapshots previous to this
snapshot will now be owned by the promoted clone. The space
they use will move from the "origin" filesystem to the promoted
clone, so is must have enough space available to accommodate
these snapshots. Note: no new space is consumed by this
operation, but the space accounting is adjusted. Also note that
the promoted clone must not have any conflicting snapshot names
of its own. The _rename_ subcommand can be used to rename any
conflicting snapshots.
in the EXAMPLES section (after 'Example 8: Creating a clone'):
Example 9: Promoting a Clone
The following commands illustrate how to test out changes to a
filesystem, and then replace the original filesystem with the
changed one, using clones, clone promotion, and renaming.
# zfs create pool/project/production
<populate /pool/project/production with data>
# zfs snapshot pool/project/[EMAIL PROTECTED]
# zfs clone pool/project/[EMAIL PROTECTED] pool/project/beta
<make changes to /pool/project/beta and test them>
# zfs promote pool/project/beta
# zfs rename pool/project/production pool/project/legacy
# zfs rename pool/project/beta pool/project/production
<once the legacy version is no longer needed, it can be
destroyed>
# zfs destroy pool/project/legacy
6. Resources and Schedule
6.4. Steering Committee requested information
6.4.1. Consolidation C-team Name:
ON
6.5. ARC review type: FastTrack
----- End forwarded message -----
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