[lvm-devel] Re: Deactivating volume with mounted snapshot

[Alasdair G Kergon]

On Wed, May 14, 2008 at 08:33:27PM -0400, Mikulas Patocka wrote:
> Basically, lvm suspends all the devices, then loads the dm table for all 
> of them and then resumes them.
 
Not strictly accurate.

You need to consider each case separately: 

  taking existing LV and adding/removing first snapshot
  adding/removing a subsequent snapshot
  activating/deactivating LV plus pre-existing snapshots

and note the sequence of significant events in each case:
  table loaded
  snapshot metadata read from disk
  filesystem quiesced
  snapshot becoming active
  etc.

Then you'd need to show that removing 'active = 1' retains correctness
in every case.  I am not convinced: Consider the case of adding a
subsequent snapshot: preload table does mem allocations, then suspend
existing LV & quiesce fs, then resume snapshot (active = 1 now) etc.
 
Alasdair
-- 
agk at redhat.com