linux-ext4 - Re: [dm-devel] Ext4 and xfs problems in dm-thin on allocation and discard

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Date:	Tue, 19 Jun 2012 17:03:01 +0100
From:	Alasdair G Kergon <agk@...hat.com>
To:	device-mapper development <dm-devel@...hat.com>
Cc:	Lukáš Czerner <lczerner@...hat.com>,
	linux-ext4@...r.kernel.org, xfs@....sgi.com,
	Spelic <spelic@...ftmail.org>
Subject: Re: [dm-devel] Ext4 and xfs problems in dm-thin on allocation and
	discard

On Tue, Jun 19, 2012 at 11:28:56AM -0400, Mike Snitzer wrote:
> That is an lvm2 BZ but there is further kernel work needed.
 
In principle, userspace should already be able to handle the replumbing I
think.  (But when we work through the details of an online import, perhaps
we'll want some further kernel change for atomicity/speed reasons?  In 
particular we need to be able to do the last part of the metadata merge
quickly.)

Roughly:
1. rejig the lvm metadata for the new configuration [lvm]
  - appends the "whole LV" data to the pool's data
2. Generate metadata for the appended data and append this to the metadata area [dmpd]
3. suspend all the affected devices [lvm]
4. link the already-prepared metadata into the existing metadata [dmpd]
5. resume all the devices (now using the new extended pool)

Alasdair

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