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Re: [dm-devel] Ext4 and xfs problems in dm-thin on allocation and discar

To: device-mapper development <dm-devel@xxxxxxxxxx>
Subject: Re: [dm-devel] Ext4 and xfs problems in dm-thin on allocation and discard
From: Alasdair G Kergon <agk@xxxxxxxxxx>
Date: Tue, 19 Jun 2012 17:03:01 +0100
Cc: Lukáš Czerner <lczerner@xxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Spelic <spelic@xxxxxxxxxxxxx>
In-reply-to: <20120619152856.GB7225@xxxxxxxxxx>
Mail-followup-to: device-mapper development <dm-devel@xxxxxxxxxx>, Lukáš Czerner <lczerner@xxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Spelic <spelic@xxxxxxxxxxxxx>
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References: <4FDF9EBE.2030809@xxxxxxxxxxxxx> <alpine.LFD.2.00.1206191601290.21961@xxxxxxxxxxxxxxxxxxxxxxxxx> <20120619141933.GC10637@xxxxxxxxx> <20120619144316.GD14208@xxxxxxxxxxxxxxxxxxxxx> <20120619152856.GB7225@xxxxxxxxxx>
User-agent: Mutt/1.5.18 (2008-05-17)
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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