From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: how do versioning filesystems take snapshot of opened files? Date: Wed, 4 Jul 2007 08:02:47 +1000 Message-ID: <18058.51079.350424.273688@notabene.brown> References: <4ae3c140707022228u2b5098c5v766b9dc9a7e09ea1@mail.gmail.com> <20070703090946.49e6062f@think.oraclecorp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: "Xin Zhao" , linux-fsdevel , linux-kernel To: Chris Mason Return-path: Received: from ns1.suse.de ([195.135.220.2]:46488 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752387AbXGCWDD (ORCPT ); Tue, 3 Jul 2007 18:03:03 -0400 In-Reply-To: message from Chris Mason on Tuesday July 3 Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tuesday July 3, chris.mason@oracle.com wrote: > > Getting a snapshot that is useful with respect to application data > requires help from the application. Certainly. > The app needs to be shutdown or > paused prior to the snapshot and then started up again after the > snapshot is taken. Alternately, the app needs to be able to cope with unexpected system shutdown (aka crash) and the same ability will allow it to cope with an atomic snapshot. It may be able to recover more efficiently from an expected shutdown, so being able to tell the app about an impending snapshot is probably a good idea, but it should be advisory only. NeilBrown