[linux-lvm] Standard Linux Framework for Snapshot Notification

[Alasdair G Kergon]

On Mon, Nov 14, 2005 at 07:20:59PM +0530, Block Device wrote:
>   I  want to know whether Linux provides any standard interface for
> volume managers etc so that applications can register themselves to be
> notified when a snapshot needs to be taken.

Not yet, but it's a reasonable thing to ask for.

> If there isnt any such interface how is consistency guaranteed for
> application data when a snapshot is taken ? eg. How does one take
> (consistent) snapshots of database instances w/o  first quiescing them
> ?
 
At the moment you have to do things the other way around:
  quiesce database
  lvcreate -s
  wake database

There already exists an in-kernel filesystem hook so that mounted filesystems 
get the notifications automatically so they can sync their metadata, and
the block devices get flushed.

Alasdair
-- 
agk at redhat.com