From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48332) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yb3lK-0004JF-DQ for qemu-devel@nongnu.org; Thu, 26 Mar 2015 05:07:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Yb3ZJ-0005D5-Dz for qemu-devel@nongnu.org; Thu, 26 Mar 2015 04:55:45 -0400 Message-ID: <5513CA2B.6010403@cn.fujitsu.com> Date: Thu, 26 Mar 2015 16:58:19 +0800 From: Wen Congyang MIME-Version: 1.0 References: <1427276174-9130-1-git-send-email-wency@cn.fujitsu.com> <1427276174-9130-2-git-send-email-wency@cn.fujitsu.com> <5512D68F.5080504@redhat.com> In-Reply-To: <5512D68F.5080504@redhat.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Qemu-block] [RFC PATCH COLO v2 01/13] docs: block replication's description List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake , qemu devel , Fam Zheng , Max Reitz , Paolo Bonzini Cc: Lai Jiangshan , qemu block , Jiang Yunhong , Dong Eddie , "Dr. David Alan Gilbert" , Gonglei , Stefan Hajnoczi , Yang Hongyang , zhanghailiang On 03/25/2015 11:38 PM, Eric Blake wrote: > On 03/25/2015 03:36 AM, Wen Congyang wrote: >> Signed-off-by: Wen Congyang >> Signed-off-by: Paolo Bonzini >> Signed-off-by: Yang Hongyang >> Signed-off-by: zhanghailiang >> Signed-off-by: Gonglei >> --- >> docs/block-replication.txt | 147 +++++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 147 insertions(+) >> create mode 100644 docs/block-replication.txt >> > > Grammar review only (I'll leave the technical review to others) > >> diff --git a/docs/block-replication.txt b/docs/block-replication.txt >> new file mode 100644 >> index 0000000..874ed8e >> --- /dev/null >> +++ b/docs/block-replication.txt >> @@ -0,0 +1,147 @@ >> +Block replication >> +---------------------------------------- >> +Copyright Fujitsu, Corp. 2015 >> +Copyright (c) 2015 Intel Corporation >> +Copyright (c) 2015 HUAWEI TECHNOLOGIES CO.,LTD. > > Space after comma in English writing. Yes, but I am not sure I can change it. HUAWEI always use this way. You can find it in bootdevice.c Thanks Wen Congyang > >> + >> +This work is licensed under the terms of the GNU GPL, version 2 or later. >> +See the COPYING file in the top-level directory. >> + >> +The block replication is used for continuous checkpoints. It is designed > > Sounds better as either of: > The block replication feature is... > Block replication is... > >> +for COLO that Secondary VM is running. It can also be applied for FT/HA > > Please define COLO and FT/HA on first use (okay to abbreviate elsewhere > in the document, but the first use should not assume the acronym is > well-known) > > s/for COLO that/for COLO (COurse-grain LOck-stepping), where the/ > >> +scene that Secondary VM is not running. > > s/for FT/HA scene that/for the FT/HA (Fault-tolerance/High Assurance) > scenario, where the/ > >> + >> +This document gives an overview of block replication's design. >> + >> +== Background == >> +High availability solutions such as micro checkpoint and COLO will do >> +consecutive checkpoint. The VM state of Primary VM and Secondary VM is > > s/checkpoint/checkpoints/ > >> +identical right after a VM checkpoint, but becomes different as the VM > ... >> + >> +4) The hidden-disk is created automatically. It buffers the original content >> +that is modified by the primary VM. It should also be an empty disk, and >> +the dirver supports bdrv_make_empty(). > > s/dirver/driver/ > >> + >> +== New block driver interface == >> +We add three block driver interfaces to control block replication: >> +a. bdrv_start_replication() >> + Start block replication, called in migration/checkpoint thread. >> + We must call bdrv_start_replication() in secondary QEMU before >> + calling bdrv_start_replication() in primary QEMU. >> +b. bdrv_do_checkpoint() >> + This interface is called after all VM state is transfered to > > s/transfered/transferred/ > >> + Secondary QEMU. The Disk buffer will be dropped in this interface. >> + The caller must hold the I/O mutex lock if it is in migration/checkpoint >> + thread. >> +c. bdrv_stop_replication() >> + It is called when failover. We will flush the Disk buffer into > > s/when/on/ > >> + Secondary Disk and stop block replication. The vm should be stopped >> + before calling it. The caller must hold the I/O mutex lock if it is >> + in migration/checkpoint thread. >> + >> +== Usage == >> +Primary: >> + -drive if=xxx,driver=quorum,read-pattern=fifo,\ >> + children.0.file.filename=1.raw,\ >> + children.0.driver=raw,\ >> + children.1.file.driver=nbd+colo,\ >> + children.1.file.host=xxx,\ >> + children.1.file.port=xxx,\ >> + children.1.file.export=xxx,\ >> + children.1.driver=raw,\ >> + children.1.ignore-errors=on > > This command line looks like multiple arguments because of the leading > whitespace on succeeding lines. I don't know if there is any better way > to format it, though, to make it obvious that it is all a single > argument to -drive. > >> + Note: >> + 1. NBD Client should not be the first child of quorum. >> + 2. There should be only one NBD Client. >> + 3. host is the secondary physical machine's hostname or IP >> + 4. Each disk must have its own export name. > > Maybe a note 5 to call out the formatting aspect of the command line? > >> + >> +Secondary: >> + -drive if=none,driver=raw,file=1.raw,id=nbd_target1 \ >> + -drive if=xxx,driver=qcow2+colo,file=active_disk.qcow2,export=xxx,\ >> + backing_reference.drive_id=nbd_target1,\ >> + backing_reference.hidden-disk.file.filename=hidden_disk.qcow2,\ >> + backing_reference.hidden-disk.driver=qcow2,\ >> + backing_reference.hidden-disk.allow-write-backing-file=on >> + Then run qmp command: >> + nbd_server_start host:port >> + Note: >> + 1. The export name for the same disk must be the same in primary >> + and secondary QEMU command line >> + 2. The qmp command nbd_server_start must be run before running the >> + qmp command migrate on primary QEMU >> + 3. Don't use nbd_server_start's other options >> + 4. Active disk, hidden disk and nbd target's length should be the >> + same. >> + 5. It is better to put active disk and hidden disk in ramdisk. >> >