Re: [PATCH 1/9] device-mapper snapshot: load metadata on creation

[Alasdair G Kergon]

On Sun, Jan 22, 2006 at 09:33:11PM -0800, Andrew Morton wrote:
> If people are using older tools and they run with this patch, what will
> happen to them?
 
The problem I have noticed is that in certain configurations LVM2 commands 
to deactivate a snapshot may fail part-way through and need to be completed
using dmsetup.

Deactivating snapshots before removing them seems to avoid that problem,
but it's not always feasible.

Example: 
  lvol1 is a snapshot of lvol0.  Both are active.
  You run 'lvremove vgg/lvol1' but the command hangs.
  Workaround: from another shell run 'dmsetup resume vgg-lvol1-cow' and
  the command then completes.

Having more than one snapshot of the same device can also lead to problems.

But without this patch and the updated LVM2 tools, whenever you run
'lvcreate -s' to create a snapshot you're taking the risk that the command 
will hang irrecoverably (leading you to want to reboot the machine even if 
it didn't panic).

Alasdair
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