From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:47027) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UekNI-0006pF-0D for qemu-devel@nongnu.org; Tue, 21 May 2013 07:05:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UekNG-0007xg-JB for qemu-devel@nongnu.org; Tue, 21 May 2013 07:04:59 -0400 Received: from smtp.maurer-it.com ([94.136.31.133]:37641 helo=proxmox.maurer-it.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UekNG-0007xF-4g for qemu-devel@nongnu.org; Tue, 21 May 2013 07:04:58 -0400 From: Dietmar Maurer Date: Tue, 21 May 2013 10:58:47 +0000 Message-ID: <24E144B8C0207547AD09C467A8259F75585982FB@lisa.maurer-it.com> References: <1368628476-19622-1-git-send-email-stefanha@redhat.com> <519479B4.6080906@linux.vnet.ibm.com> <20130516074746.GF1597@stefanha-thinkpad.redhat.com> <519603C1.5060104@redhat.com> <5199CF7F.3060507@redhat.com> <20130521073159.GA30951@stefanha-thinkpad.muc.redhat.com> <519B309E.6020201@redhat.com> <20130521103413.GA19747@stefanha-thinkpad.muc.redhat.com> <519B4E31.6040503@redhat.com> In-Reply-To: <519B4E31.6040503@redhat.com> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , Stefan Hajnoczi Cc: Kevin Wolf , Fam Zheng , Stefan Hajnoczi , qemu-devel , "imain@redhat.com" , Wenchao Xia > >> True, but that would happen only in case the host crashes. Even for > >> a QEMU crash the changes would be safe, I think. They would be > >> written back when the persistent dirty bitmap's mmap() area is > >> unmapped, during process exit. > > > > I'd err on the side of caution, mark the persistent dirty bitmap while > > QEMU is running. Discard the file if there was a power failure. >=20 > Agreed. Though this is something that management must do manually, isn't= it? > QEMU cannot distinguish a SIGKILL from a power failure, while management > can afford treating SIGKILL as a power failure. >=20 > > It really depends what the dirty bitmap users are doing. It could be > > okay to have a tiny chance of missing a modification but it might not. I just want to mention that there is another way to do incremental backups.= Instead of using a dirty bitmap, you can compare the content, usually using a diges= t (SHA1) on clusters. That way you can also implement async replication to a remote site (like MS= do).