From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: [PATCH 1/3] fs: Document the reflink(2) system call. Date: Tue, 12 May 2009 20:40:39 +0100 Message-ID: <20090512194039.GD10436@shareable.org> References: <1241530798.7244.65.camel@think.oraclecorp.com> <20090505153629.GB31100@shareable.org> <1241538102.7244.72.camel@think.oraclecorp.com> <20090505160313.GF31100@shareable.org> <4A00A634.4020008@hp.com> <20090505215711.GA7574@shareable.org> <20090505220459.GN7835@mail.oracle.com> <20090505221236.GE7574@shareable.org> <20090505222131.GO7835@mail.oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Joel Becker , jim owens , Chris Mason , Theodore Tso , linux-fsdevel@vger.kernel.org, ocfs2-devel@oss.oracle.com, viro@zeniv.linux.org.uk, "Daniel P. Berrange" To: James Morris Return-path: Received: from mail2.shareable.org ([80.68.89.115]:35662 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751888AbZELTkq (ORCPT ); Tue, 12 May 2009 15:40:46 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: James Morris wrote: > Indeed... I think a great use-case scenario for this will be snapshotting > VM images, as well as fast and space-efficient instantiation of VMs. I agree, except beware of the illusion that atomic file snapshots mean safe VM snapshots... To snapshot a live VM safely, you need to atomically snapshot both the running state (memory and CPU) _and_ all its disk images simultaneously. Otherwise you're asking for guest filesystem corruption. reflink() won't do that by itself, but the VM implementation could use reflink() to make fast snapshots without significantly pausing a running VM. -- Jamie