[linux-lvm] Standard Linux Framework for Snapshot Notification

[linux-lvm] Standard Linux Framework for Snapshot Notification

[Block Device]

Hi,

  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.
Something similar to VSS on Windows.

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
?

If this not the right place to ask this, can someone point me in the
right direction ?

Thanks & Regards
BD.

Re: [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@redhat.com

Re: [linux-lvm] Standard Linux Framework for Snapshot Notification

[Block Device]

 Hi Alasdair,

> 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.

What hook is that ? Could you please elaborate and explain how it works :) ?

Thanks
BD :)