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

[Alasdair G Kergon <agk redhat com>]

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