From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mr014msb.fastweb.it ([85.18.95.103]:39228 "EHLO mr014msb.fastweb.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751449AbeBXW5f (ORCPT ); Sat, 24 Feb 2018 17:57:35 -0500 Subject: Re: Reflink (cow) copy of busy files MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Sat, 24 Feb 2018 23:57:32 +0100 From: Gionatan Danti In-Reply-To: <20180224220757.GC30854@dastard> References: <9e69fcd01e1c02ea53e0e1ac66d60d24@assyoma.it> <20180224220757.GC30854@dastard> Message-ID: <711dd96e3c4b3e92d3fb38a01e77dc64@assyoma.it> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Dave Chinner Cc: linux-xfs@vger.kernel.org, g.danti@assyoma.it Il 24-02-2018 23:07 Dave Chinner ha scritto: > Define "busy file", please. Think about a running virtual machine. Maybe an XFS-based virtual image (ie: a CentOS 7 guest). > If the file is being actively written, then the clone will not be > consistent. > > Yes, it's just like any other snapshot process - you have to quiesce > everything that is writing to the file before cloning it. i.e. the > data in the file needs to be in a stable, consistent, unchanging > state if you want the clone to contain consistent data... About *what* level of consistency are we speaking? I understand that application-level consistency requires a quiesced filesystem and, possibly, an application-level agent. But is it a quiesced filesystem a requisite for a *crash-consistent* ie: pull the plug) snapshot? In other words: would a cp --reflink=always of a runnig virtual machine produce an usable, crash-consistent snapshot, or it risks ending with binary garbage? Thanks. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8