Re: [zfs-discuss] fwd: ZFS Clone Promotion [PSARC/2006/303 Timeout: 05/12/2006]

[Lori Alt]

So let me work through a scenario of how clone promotion might work in conjunction with liveupgrade once we have bootable zfs datasets: 1.  We are booted off the dataset  pool/root_sol10_u4 2.  We want to upgrade to U5.  So we begin by lucreating a new       boot environment (BE) as a clone of the current root        #  lucreate -n root_sol10_u5 -m /:pool/root_sol10_u4:zfs        By default, liveupgrade will use zfs cloning when creating a new        BE from an existing zfs dataset.  So behind the scenes, lucreate        will execute:        # zfs snapshot pool/[EMAIL PROTECTED]        # zfs clone pool/[EMAIL PROTECTED] pool/root_sol10_u5         (this will take only seconds, and require no pre-allocated space) 3.  Now we do the luupgrade of the newly lucreate'd BE to U5.      Note that the only space required for the upgrade is the      space needed for packages that are new or  modified in U5. 4.  So the administrator tries out the new BE by luactivate'ing it      and booting it.  (This is where we need a menu'ing interface      at boot time, so we can choose between the various bootable      datasets in the pool.  Conveniently, GRUB provides us with one.) 5.  The new BE works fine, so the administrator decides to promote      the BE's dataset (which is still a clone) to primary dataset status.      Here I'm not sure what's best:  should liveupgrade promote the      dataset as part of its management of boot environments?  Or      should the administrator have to (or be able to) promote a      a bootable dataset explicitly?  I'll have to give that one a bit of      thought, but one way or another, this happens:      #  zfs promote pool/root_sol10_u5 6.   So we can rename the newly-promoted BE if we want, but let's       assume we leave it with its name "root_sol10_u5".  Now if we       want to get rid of the old U4 root dataset, we should do the       following:        # ludelete root_sol10_u4        which, in addition to the usual liveupgrade tasks to delete the        BE, will do this:        # zfs destroy pool/root_sol10_u4 So, for the purposes of zfs boot and liveupgrade, I think your new "promote" function works very well.  Am I missing anything? Lori       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 ----- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss

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