From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Question: data consistency on fail-over using shared disk Date: Wed, 21 Jul 2010 13:46:27 +0300 Message-ID: <4C46D003.5030300@redhat.com> References: <4C469350.3080008@oss.ntt.co.jp> <4C46A179.4070400@redhat.com> <4C46A505.4000503@oss.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Cc: KVM list To: Takuya Yoshikawa Return-path: Received: from mx1.redhat.com ([209.132.183.28]:1025 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751044Ab0GUKqd (ORCPT ); Wed, 21 Jul 2010 06:46:33 -0400 In-Reply-To: <4C46A505.4000503@oss.ntt.co.jp> Sender: kvm-owner@vger.kernel.org List-ID: On 07/21/2010 10:43 AM, Takuya Yoshikawa wrote: > >> If the VM can't do anything, you're safe. Of course a crash doesn't mean >> a VM can't do anything, you typically need to isolate it by resetting >> the host or having a switch disconnect its storage and network. >> >> > Thanks, > We are starting to manage the "only VM crashed" case by HA. > So yes, we need to reset the host. > It may be sufficient to issue a sync(2). >> I believe nothing special is needed, as long as a crash means both the >> qemu and host kernel crashed. If only qemu crashed, then the writeback >> case needs buffers flushed. >> >> > My main concern is only qemu crashed and host is alive case. > > Host memory is typically large, so we want to eliminate flushing everything > if possible. > > So we don't need to flush in the case of writethrough = RHEL default ? > No. But you do need to unmount the underlying host filesystem. I recommend using cache=none and direct volume access, this is easier to guarantee integrity. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.