From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Durgin Subject: Re: snapshot storage use Date: Tue, 17 Jul 2012 11:17:56 -0700 Message-ID: <5005AC54.6030708@inktank.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-gh0-f174.google.com ([209.85.160.174]:44078 "EHLO mail-gh0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756211Ab2GQSUO (ORCPT ); Tue, 17 Jul 2012 14:20:14 -0400 Received: by ghrr11 with SMTP id r11so702252ghr.19 for ; Tue, 17 Jul 2012 11:20:14 -0700 (PDT) In-Reply-To: Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Travis Rhoden Cc: ceph-devel@vger.kernel.org On 07/17/2012 11:11 AM, Travis Rhoden wrote: > Hey folks, > > Sorry if this info is covered elsewhere -- I searched but was unable > to find a description of what I wanted. > > Roughly how much storage is used by snapshots? Is it really just > marking the version of certain objects, such that multiple snapshots > of the same (unchanged) object consume essentially no new space? > Correspondingly, once that object is finally modified, it is copied > and the snapshots still point to the original (old) copy? Is this > done by using hardlinks or some other method? Yes, snapshots are copy-on-write at the object level. On the osd, this is either an efficient clone (btrfs) or a full copy of the object (non-btrfs). > > Just wanted the 10,000 foot view explanation. =) > > Thanks, > > - Travis