From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx3.redhat.com (mx3.redhat.com [172.16.48.32]) by int-mx1.corp.redhat.com (8.11.6/8.11.6) with ESMTP id iAJH5Rr15420 for ; Fri, 19 Nov 2004 12:05:27 -0500 Received: from email.careercast.com (email.careercast.com [216.39.101.233]) by mx3.redhat.com (8.12.11/8.12.11) with SMTP id iAJH5LB8004643 for ; Fri, 19 Nov 2004 12:05:21 -0500 Subject: Re: [linux-lvm] relocate on write for snapshot From: Clint Byrum In-Reply-To: <1100882347.2984.32.camel@localhost.localdomain> References: <1100882347.2984.32.camel@localhost.localdomain> Date: Fri, 19 Nov 2004 09:05:20 -0800 Message-Id: <1100883920.16306.2.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" To: mingz@ele.uri.edu, LVM general discussion and development On Fri, 2004-11-19 at 11:39 -0500, Ming Zhang wrote: > Hi, I wonder if there are any thought about a relocate on write policy > for snapshot instead of copy on write policy used now? > > instead of copy old one to snapshot, overwrite old one with new one, 2 > writes and 1 reads. it is possible that write new data to a usused > location directly. > > i know later remove a snaphot will be a little trouble, but there must > be some way to get around it. > > just a rough thought, any comment? > I thought the way it worked now was for snapshot LV to be marked as the "active destination" for all new writes to the logical volume. On write, the data isn't copied, just the metadata is changed to reflect which physical extent the block is now located on, and the old one is then reallocated as part of the snapshot. Am I wrong? -- Clint Byrum