[linux-lvm] LVM multiple Snpshots implementation query

andiket a truly_linux at yahoo.co.in
Tue May 11 06:38:48 UTC 2010

Thanks a lot.
I wasnt of the patch.

Yes, I am looking for a similar thing.
Right now after snapshot the cow is done for all the snapshots if there is a write on origin.

This is an obvious thing. Wondering it was missed in original lvm/dm snapshot code.

Any idea?

--- On Tue, 11/5/10, Busby.Cheung <chaimvy at 163.com> wrote:

From: Busby.Cheung <chaimvy at 163.com>
Subject: Re: [linux-lvm] LVM multiple Snpshots implementation query
To: "LVM general discussion and development" <linux-lvm at redhat.com>
Date: Tuesday, 11 May, 2010, 7:44 AM

Did you mean you want to use something like shared-snapshot? COW once?
I know shared-snapshot implemented by Mikulas and others:

在2010-05-10,"andiket a" <truly_linux at yahoo.co.in> 写道: 
发件人:"andiket a" <truly_linux at yahoo.co.in>
发送时间:2010年5月10日 星期一
收件人:linux-lvm at redhat.com
主题:[linux-lvm] LVM multiple Snpshots implementation query


If there are multiple snapshots then write to origin is an expensive operation.
My understanding after looking at the code of orig_wirte() is that if a write comes on a chunk on orig device then cow is initiated for all the snapshots.
This is an expensive operation for sure.

Does anyone know if there was any reason behind implementing it like this?



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