> -----Original Message-----
> From: Lukas Straub <lukasstra...@web.de>
> Sent: Saturday, September 28, 2019 9:25 PM
> To: Zhang, Chen <chen.zh...@intel.com>
> Cc: qemu-devel <qemu-devel@nongnu.org>; Jason Wang
> <jasow...@redhat.com>; Wen Congyang <wencongya...@huawei.com>;
> Xie Changlong <xiechanglon...@gmail.com>; kw...@redhat.com;
> mre...@redhat.com
> Subject: Re: [PATCH v5 4/4] colo: Update Documentation for continuous
> replication
>
> On Thu, 26 Sep 2019 17:27:35 +0000
> "Zhang, Chen" <chen.zh...@intel.com> wrote:
>
> > > -----Original Message-----
> > > From: Lukas Straub <lukasstra...@web.de>
> > > Sent: Monday, September 16, 2019 3:20 AM
> > > To: qemu-devel <qemu-devel@nongnu.org>
> > > Cc: Zhang, Chen <chen.zh...@intel.com>; Jason Wang
> > > <jasow...@redhat.com>; Wen Congyang
> <wencongya...@huawei.com>; Xie
> > > Changlong <xiechanglon...@gmail.com>; kw...@redhat.com;
> > > mre...@redhat.com
> > > Subject: [PATCH v5 4/4] colo: Update Documentation for continuous
> > > replication
> > >
> > > Document the qemu command-line and qmp commands for continuous
> > > replication
> > >
> > > Signed-off-by: Lukas Straub <lukasstra...@web.de>
> > > ---
> > > docs/COLO-FT.txt | 212 +++++++++++++++++++++++++++----------
> > > docs/block-replication.txt | 28 +++--
> > > 2 files changed, 173 insertions(+), 67 deletions(-)
> > >
> > > diff --git a/docs/COLO-FT.txt b/docs/COLO-FT.txt index
> > > ad24680d13..e98c95ca2b 100644
> > > --- a/docs/COLO-FT.txt
> > > +++ b/docs/COLO-FT.txt
> > > @@ -145,35 +145,65 @@ The diagram just shows the main qmp
> command,
> > > you can get the detail in test procedure.
> > >
> > > == Test procedure ==
> > > -1. Startup qemu
> > > -Primary:
> > > -# qemu-system-x86_64 -accel kvm -m 2048 -smp 2 -qmp stdio -name
> > > primary \
> > > - -device piix3-usb-uhci -vnc :7 \
> > > - -device usb-tablet -netdev tap,id=hn0,vhost=off \
> > > - -device virtio-net-pci,id=net-pci0,netdev=hn0 \
> > > - -drive
> > > if=virtio,id=primary-disk0,driver=quorum,read-pattern=fifo,vote-
> > > threshold=1,\
> > > - children.0.file.filename=1.raw,\
> > > - children.0.driver=raw -S
> > > -Secondary:
> > > -# qemu-system-x86_64 -accel kvm -m 2048 -smp 2 -qmp stdio -name
> > > secondary \
> > > - -device piix3-usb-uhci -vnc :7 \
> > > - -device usb-tablet -netdev tap,id=hn0,vhost=off \
> > > - -device virtio-net-pci,id=net-pci0,netdev=hn0 \
> > > - -drive
> > > if=none,id=secondary-disk0,file.filename=1.raw,driver=raw,node-
> > > name=node0 \
> > > - -drive if=virtio,id=active-disk0,driver=replication,mode=secondary,\
> > > - file.driver=qcow2,top-id=active-disk0,\
> > > - file.file.filename=/mnt/ramfs/active_disk.img,\
> > > - file.backing.driver=qcow2,\
> > > - file.backing.file.filename=/mnt/ramfs/hidden_disk.img,\
> > > - file.backing.backing=secondary-disk0 \
> > > - -incoming tcp:0:8888
> > > -
> > > -2. On Secondary VM's QEMU monitor, issue command
> > > +Note: Here we are running both instances on the same Machine for
> > > +testing, change the IP Addresses if you want to run it on two Hosts
> > > +
> > > +== Startup qemu ==
> > > +1. Primary:
> > > +# imagefolder="/mnt/vms/colo-test"
> > > +
> > > +The disks for the primary and secondary need to be the same before
> > > +starting colo # cp --reflink=auto $imagefolder/primary.qcow2
> > > +$imagefolder/primary-copy.qcow2
> > > +
> > > +# qemu-system-x86_64 -enable-kvm -cpu qemu64,+kvmclock -m 512 -
> smp
> > > 1 -qmp stdio \
> > > + -vnc :0 -device piix3-usb-uhci -device usb-tablet -name primary \
> > > + -netdev
> > > + tap,id=hn0,vhost=off,helper=/usr/lib/qemu/qemu-bridge-helper
> > > \
> > > + -device rtl8139,id=e0,netdev=hn0 \
> > > + -chardev socket,id=mirror0,host=127.0.0.1,port=9003,server,nowait \
> > > + -chardev socket,id=compare1,host=127.0.0.1,port=9004,server,wait \
> > > + -chardev socket,id=compare0,host=127.0.0.1,port=9001,server,nowait
> \
> > > + -chardev socket,id=compare0-0,host=127.0.0.1,port=9001 \
> > > + -chardev
> > > + socket,id=compare_out,host=127.0.0.1,port=9005,server,nowait
> > > \
> > > + -chardev socket,id=compare_out0,host=127.0.0.1,port=9005 \
> > > + -object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0 \
> > > + -object filter-
> > > redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out \
> > > + -object filter-
> > > redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0 \
> > > + -object iothread,id=iothread1 \
> > > + -object
> > > +colo-compare,id=comp0,primary_in=compare0-
> > > 0,secondary_in=compare1,\
> > > +outdev=compare_out0,iothread=iothread1 \
> > > + -drive
> > > +if=ide,id=colo-disk0,driver=quorum,read-pattern=fifo,vote-threshold
> > > +=1,\
> > > +children.0.file.filename=$imagefolder/primary.qcow2,children.0.driv
> > > +er=q
> > > +cow2 -S
> > > +
> > > +2. Secondary:
> > > +# imagefolder="/mnt/vms/colo-test"
> > > +
> > > +# qemu-img create -f qcow2 $imagefolder/secondary-active.qcow2 10G
> > > +
> > > +# qemu-img create -f qcow2 $imagefolder/secondary-hidden.qcow2
> 10G
> > > +
> > > +# qemu-system-x86_64 -enable-kvm -cpu qemu64,+kvmclock -m 512 -
> smp
> > > 1 -qmp stdio \
> > > + -vnc :1 -device piix3-usb-uhci -device usb-tablet -name secondary \
> > > + -netdev
> > > + tap,id=hn0,vhost=off,helper=/usr/lib/qemu/qemu-bridge-helper
> > > \
> > > + -device rtl8139,id=e0,netdev=hn0 \
> > > + -chardev socket,id=red0,host=127.0.0.1,port=9003,reconnect=1 \
> > > + -chardev socket,id=red1,host=127.0.0.1,port=9004,reconnect=1 \
> > > + -object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0 \
> > > + -object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1 \
> > > + -object filter-rewriter,id=rew0,netdev=hn0,queue=all \
> > > + -drive if=none,id=parent0,file.filename=$imagefolder/primary-
> > > copy.qcow2,driver=qcow2 \
> > > + -drive
> > > +if=none,id=childs0,driver=replication,mode=secondary,file.driver=qc
> > > +ow2,
> > > +\
> > > +top-id=childs0,file.file.filename=$imagefolder/secondary-active.qco
> > > +w2,\
> > > +file.backing.driver=qcow2,file.backing.file.filename=$imagefolder/s
> > > +econ
> > > +dary-hidden.qcow2,\
> > > +file.backing.backing=parent0 \
> > > + -drive
> > > +if=ide,id=colo-disk0,driver=quorum,read-pattern=fifo,vote-threshold
> > > +=1,\
> > > +children.0=childs0 \
> > > + -incoming tcp:0:9998
> > > +
> >
> > I know in your COLO test environment, all the node running in same
> > physical machine, but current COLO start parameter demo easy to
> misunderstand users.
> > I think we can introduce primary node as 192.168.1.1, secondary node as
> 192.168.1.2.
> > Same issue for the VM image, we should avoid the "primary-copy.qow2".
> > Make two node independent is more clear.
> >
>
> Ok, I will remove the primary-copy stuff. But I have a better idea for the IP
> addresses:
> Using 127.0.0.1 for Primary and 127.0.0.2 for Secondary. Both point to
> localhost, making quick testing by simple copy-paste possible when using
> different values for the imagefolder Variable. At the same time Users see
> which IP to substitute for the remote node when using multiple Hosts and
> we avoid the confusion with primary-copy.
> What do you think?
>
I think it is a good idea~
Thanks
Zhang Chen
> >
> > > +
> > > +3. On Secondary VM's QEMU monitor, issue command
> > > {'execute':'qmp_capabilities'}
> > > -{ 'execute': 'nbd-server-start',
> > > - 'arguments': {'addr': {'type': 'inet', 'data': {'host': 'xx.xx.xx.xx',
> > > 'port':
> > > '8889'} } } -}
> > > -{'execute': 'nbd-server-add', 'arguments': {'device':
> > > 'secondary-disk0',
> > > 'writable': true } }
> > > +{'execute': 'nbd-server-start', 'arguments': {'addr': {'type':
> > > +'inet',
> > > +'data': {'host': '127.0.0.1', 'port': '9999'} } } }
> > > +{'execute': 'nbd-server-add', 'arguments': {'device': 'parent0',
> > > +'writable': true } }
> > >
> > > Note:
> > > a. The qmp command nbd-server-start and nbd-server-add must be
> > > run @@ -182,44 +212,112 @@ Note:
> > > same.
> > > c. It is better to put active disk and hidden disk in ramdisk.
> > >
> > > -3. On Primary VM's QEMU monitor, issue command:
> > > +4. On Primary VM's QEMU monitor, issue command:
> > > {'execute':'qmp_capabilities'}
> > > -{ 'execute': 'human-monitor-command',
> > > - 'arguments': {'command-line': 'drive_add -n buddy
> > > driver=replication,mode=primary,file.driver=nbd,file.host=xx.xx.xx.x
> > > x,file.p
> > > ort=8889,file.export=secondary-disk0,node-name=nbd_client0'}}
> > > -{ 'execute':'x-blockdev-change', 'arguments':{'parent':
> > > 'primary-disk0',
> > > 'node': 'nbd_client0' } } -{ 'execute': 'migrate-set-capabilities',
> > > - 'arguments': {'capabilities': [ {'capability': 'x-colo', 'state':
> > > true } ] } }
> > > -{ 'execute': 'migrate', 'arguments': {'uri': 'tcp:xx.xx.xx.xx:8888'
> > > } }
> > > +{'execute': 'human-monitor-command', 'arguments': {'command-line':
> > > +'drive_add -n buddy
> > > +driver=replication,mode=primary,file.driver=nbd,file.host=127.0.0.1
> > > +,fil e.port=9999,file.export=parent0,node-name=replication0'}}
> > > +{'execute': 'x-blockdev-change', 'arguments':{'parent':
> > > +'colo-disk0',
> > > +'node': 'replication0' } }
> > > +{'execute': 'migrate-set-capabilities', 'arguments':
> > > +{'capabilities': [
> > > +{'capability': 'x-colo', 'state': true } ] } }
> > > +{'execute': 'migrate', 'arguments': {'uri': 'tcp:127.0.0.1:9998' }
> > > +}
> > >
> > > Note:
> > > a. There should be only one NBD Client for each primary disk.
> > > - b. xx.xx.xx.xx is the secondary physical machine's hostname or IP
> > > - c. The qmp command line must be run after running qmp command
> > > line in
> > > + b. The qmp command line must be run after running qmp command
> > > + line in
> > > secondary qemu.
> > >
> > > -4. After the above steps, you will see, whenever you make changes
> > > to PVM, SVM will be synced.
> > > +5. After the above steps, you will see, whenever you make changes
> > > +to PVM,
> > > SVM will be synced.
> > > You can issue command '{ "execute": "migrate-set-parameters" ,
> > > "arguments":{ "x-checkpoint-delay": 2000 } }'
> > > -to change the checkpoint period time
> > > +to change the idle checkpoint period time
> > > +
> > > +6. Failover test
> > > +You can kill one of the VMs and Failover on the surviving VM:
> > > +
> > > +If you killed the Secondary, then follow "Primary Failover". After
> > > +that, if you want to resume the replication, follow "Primary resume
> > > replication"
> > > +
> > > +If you killed the Primary, then follow "Secondary Failover". After
> > > +that, if you want to resume the replication, follow "Secondary
> > > +resume
> > > replication"
> > > +
> > > +== Primary Failover ==
> > > +The Secondary died, resume on the Primary
> > > +
> > > +{'execute': 'x-blockdev-change', 'arguments':{ 'parent':
> > > +'colo-disk0',
> > > +'child': 'children.1'} }
> > > +{'execute': 'human-monitor-command', 'arguments':{ 'command-line':
> > > +'drive_del replication0' } }
> > > +{'execute': 'object-del', 'arguments':{ 'id': 'comp0' } }
> > > +{'execute': 'object-del', 'arguments':{ 'id': 'iothread1' } }
> > > +{'execute': 'object-del', 'arguments':{ 'id': 'm0' } }
> > > +{'execute': 'object-del', 'arguments':{ 'id': 'redire0' } }
> > > +{'execute': 'object-del', 'arguments':{ 'id': 'redire1' } }
> > > +{'execute': 'x-colo-lost-heartbeat' }
> > > +
> > > +== Secondary Failover ==
> > > +The Primary died, resume on the Secondary and prepare to become the
> > > new
> > > +Primary
> > > +
> > > +{'execute': 'nbd-server-stop'}
> > > +{'execute': 'x-colo-lost-heartbeat'}
> > > +
> > > +{'execute': 'object-del', 'arguments':{ 'id': 'f2' } }
> > > +{'execute': 'object-del', 'arguments':{ 'id': 'f1' } }
> > > +{'execute': 'chardev-remove', 'arguments':{ 'id': 'red1' } }
> > > +{'execute': 'chardev-remove', 'arguments':{ 'id': 'red0' } }
> > > +
> > > +{'execute': 'chardev-add', 'arguments':{ 'id': 'mirror0', 'backend':
> > > +{'type': 'socket', 'data': {'addr': { 'type': 'inet', 'data': { 'host':
> > > +'127.0.0.1', 'port': '9003' } }, 'server': true } } } }
> > > +{'execute': 'chardev-add', 'arguments':{ 'id': 'compare1', 'backend':
> > > +{'type': 'socket', 'data': {'addr': { 'type': 'inet', 'data': { 'host':
> > > +'127.0.0.1', 'port': '9004' } }, 'server': true } } } }
> > > +{'execute': 'chardev-add', 'arguments':{ 'id': 'compare0', 'backend':
> > > +{'type': 'socket', 'data': {'addr': { 'type': 'inet', 'data': { 'host':
> > > +'127.0.0.1', 'port': '9001' } }, 'server': true } } } }
> > > +{'execute': 'chardev-add', 'arguments':{ 'id': 'compare0-0', 'backend':
> > > +{'type': 'socket', 'data': {'addr': { 'type': 'inet', 'data': { 'host':
> > > +'127.0.0.1', 'port': '9001' } }, 'server': false } } } }
> > > +{'execute': 'chardev-add', 'arguments':{ 'id': 'compare_out',
> > > +'backend': {'type': 'socket', 'data': {'addr': { 'type': 'inet',
> > > +'data': { 'host': '127.0.0.1', 'port': '9005' } }, 'server': true }
> > > +} } }
> > > +{'execute': 'chardev-add', 'arguments':{ 'id': 'compare_out0',
> > > +'backend': {'type': 'socket', 'data': {'addr': { 'type': 'inet',
> > > +'data': { 'host': '127.0.0.1', 'port': '9005' } }, 'server': false
> > > +} } } }
> > > +
> > > +== Primary resume replication ==
> > > +Resume replication after new Secondary is up.
> > > +
> > > +Start the new Secondary (Steps 2 and 3 above), then:
> >
> > Please note here the "then" is the original secondary node.
> > It is easy to misunderstand here.
>
> Ok, I will make this more clear.
>
> > > +{'execute': 'drive-mirror', 'arguments':{ 'device': 'colo-disk0',
> > > +'job-id': 'resync', 'target': 'nbd://127.0.0.1:9999/parent0', 'mode':
> > > +'existing', 'format': 'raw', 'sync': 'full'} }
> > > +
> >
> > As I mentioned before, the 'nbd://127.0.0.1:9999/parent0' is very confusing,
> user don't know which node will be connected.
> >
> > > +Wait until disk is synced, then:
> > > +{'execute': 'stop'}
> > > +{'execute': 'block-job-cancel', 'arguments':{ 'device': 'resync'} }
> > > +
> > > +{'execute': 'human-monitor-command', 'arguments':{ 'command-line':
> > > +'drive_add -n buddy
> > > +driver=replication,mode=primary,file.driver=nbd,file.host=127.0.0.1
> > > +,fil e.port=9999,file.export=parent0,node-name=replication0'}}
> > > +{'execute': 'x-blockdev-change', 'arguments':{ 'parent':
> > > +'colo-disk0',
> > > +'node': 'replication0' } }
> > > +
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type':
> > > +'filter-mirror',
> > > +'id': 'm0', 'props': { 'netdev': 'hn0', 'queue': 'tx', 'outdev':
> > > +'mirror0' } } }
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type':
> > > +'filter-redirector', 'id': 'redire0', 'props': { 'netdev': 'hn0',
> > > +'queue': 'rx', 'indev': 'compare_out' } } }
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type':
> > > +'filter-redirector', 'id': 'redire1', 'props': { 'netdev': 'hn0',
> > > +'queue': 'rx', 'outdev': 'compare0' } } }
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type': 'iothread', 'id':
> > > +'iothread1' } }
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type': 'colo-compare',
> > > +'id': 'comp0', 'props': { 'primary_in': 'compare0-0', 'secondary_in':
> > > +'compare1', 'outdev': 'compare_out0', 'iothread': 'iothread1' } } }
> > > +
> > > +{'execute': 'migrate-set-capabilities', 'arguments':{
> > > +'capabilities': [
> > > +{'capability': 'x-colo', 'state': true } ] } }
> > > +{'execute': 'migrate', 'arguments':{ 'uri': 'tcp:127.0.0.1:9998' }
> > > +}
> > > +
> >
> > The guest network have issues here in my test, I can't ping the guest from
> the host.
> > Is it works in your test environment?
>
> Yes, it works for me (based on v4.1.0). I simply copy-paste everything here
> 1:1 for testing.
>
> Regards,
> Lukas Straub
>
> > By the way, after finish this doc we can sync it to Qemu COLO WIKI page.
> >
> > Thanks
> > Zhang Chen
> >
> >
> > > +Note:
> > > +If this Primary previously was a Secondary, then we need to insert
> > > +the filters before the filter-rewriter by using the
> > > +"'insert': 'before', 'position': 'rew0'" Options. See below.
> > > +
> > > +== Secondary resume replication ==
> > > +Become Primary and resume replication after new Secondary is up.
> > > +
> > > +Start the new Secondary (Steps 2 and 3 above, but with different
> > > +image than
> > > +primary-copy.qcow2 and different VNC port), then:
> > > +{'execute': 'drive-mirror', 'arguments':{ 'device': 'colo-disk0',
> > > +'job-id': 'resync', 'target': 'nbd://127.0.0.1:9999/parent0', 'mode':
> > > +'existing', 'format': 'raw', 'sync': 'full'} }
> > > +
> > > +Wait until disk is synced, then:
> > > +{'execute': 'stop'}
> > > +{'execute': 'block-job-cancel', 'arguments':{ 'device': 'resync' }
> > > +}
> > >
> > > -5. Failover test
> > > -You can kill Primary VM and run 'x_colo_lost_heartbeat' in
> > > Secondary VM's - monitor at the same time, then SVM will failover
> > > and client will not detect this -change.
> > > +{'execute': 'human-monitor-command', 'arguments':{ 'command-line':
> > > +'drive_add -n buddy
> > > +driver=replication,mode=primary,file.driver=nbd,file.host=127.0.0.1
> > > +,fil e.port=9999,file.export=parent0,node-name=replication0'}}
> > > +{'execute': 'x-blockdev-change', 'arguments':{ 'parent':
> > > +'colo-disk0',
> > > +'node': 'replication0' } }
> > >
> > > -Before issuing '{ "execute": "x-colo-lost-heartbeat" }' command, we
> > > have to -issue block related command to stop block replication.
> > > -Primary:
> > > - Remove the nbd child from the quorum:
> > > - { 'execute': 'x-blockdev-change', 'arguments': {'parent': 'colo-disk0',
> 'child':
> > > 'children.1'}}
> > > - { 'execute': 'human-monitor-command','arguments': {'command-line':
> > > 'drive_del blk-buddy0'}}
> > > - Note: there is no qmp command to remove the blockdev now
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type':
> > > +'filter-mirror',
> > > +'id': 'm0', 'props': { 'insert': 'before', 'position': 'id=rew0',
> > > +'netdev': 'hn0', 'queue': 'tx', 'outdev': 'mirror0' } } }
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type':
> > > +'filter-redirector', 'id': 'redire0', 'props': { 'insert':
> > > +'before',
> > > +'position': 'id=rew0', 'netdev': 'hn0', 'queue': 'rx', 'indev':
> > > +'compare_out' } } }
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type':
> > > +'filter-redirector', 'id': 'redire1', 'props': { 'insert':
> > > +'before',
> > > +'position': 'id=rew0', 'netdev': 'hn0', 'queue': 'rx', 'outdev':
> > > +'compare0' } } }
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type': 'iothread', 'id':
> > > +'iothread1' } }
> > > +{'execute': 'object-add', 'arguments':{ 'qom-type': 'colo-compare',
> > > +'id': 'comp0', 'props': { 'primary_in': 'compare0-0', 'secondary_in':
> > > +'compare1', 'outdev': 'compare_out0', 'iothread': 'iothread1' } } }
> > >
> > > -Secondary:
> > > - The primary host is down, so we should do the following thing:
> > > - { 'execute': 'nbd-server-stop' }
> > > +{'execute': 'migrate-set-capabilities', 'arguments':{
> > > +'capabilities': [
> > > +{'capability': 'x-colo', 'state': true } ] } }
> > > +{'execute': 'migrate', 'arguments':{ 'uri': 'tcp:127.0.0.1:9998' }
> > > +}
> > >
> > > == TODO ==
> > > -1. Support continuous VM replication.
> > > -2. Support shared storage.
> > > -3. Develop the heartbeat part.
> > > -4. Reduce checkpoint VM’s downtime while doing checkpoint.
> > > +1. Support shared storage.
> > > +2. Develop the heartbeat part.
> > > +3. Reduce checkpoint VM’s downtime while doing checkpoint.
> > > diff --git a/docs/block-replication.txt b/docs/block-replication.txt
> > > index
> > > 6bde6737fb..108e9166a8 100644
> > > --- a/docs/block-replication.txt
> > > +++ b/docs/block-replication.txt
> > > @@ -65,12 +65,12 @@ blocks that are already in QEMU.
> > > ^ || .----------
> > > | || | Secondary
> > > 1 Quorum || '----------
> > > - / \ ||
> > > - / \ ||
> > > - Primary 2 filter
> > > - disk ^
> > > virtio-blk
> > > - |
> > > ^
> > > - 3 NBD -------> 3 NBD
> > > |
> > > + / \ ||
> > > virtio-blk
> > > + / \ ||
> > > ^
> > > + Primary 2 filter
> > > |
> > > + disk ^
> > > 7 Quorum
> > > + |
> > > /
> > > + 3 NBD -------> 3 NBD
> > > /
> > > client || server
> > > 2 filter
> > > || ^
> > > ^
> > > --------. || |
> > > |
> > > @@ -106,6 +106,10 @@ any state that would otherwise be lost by the
> > > speculative write-through of the NBD server into the secondary
> > > disk. So before block replication, the primary disk and secondary
> > > disk should contain the same data.
> > >
> > > +7) The secondary also has a quorum node, so after secondary
> > > +failover it can become the new primary and continue replication.
> > > +
> > > +
> > > == Failure Handling ==
> > > There are 7 internal errors when block replication is running:
> > > 1. I/O error on primary disk
> > > @@ -171,16 +175,18 @@ Primary:
> > > leading whitespace.
> > > 5. The qmp command line must be run after running qmp command line
> in
> > > secondary qemu.
> > > - 6. After failover we need remove children.1 (replication driver).
> > > + 6. After primary failover we need remove children.1 (replication
> > > driver).
> > >
> > > Secondary:
> > > -drive if=none,driver=raw,file.filename=1.raw,id=colo1 \
> > > - -drive if=xxx,id=topxxx,driver=replication,mode=secondary,top-
> > > id=topxxx\
> > > + -drive
> > > + if=none,id=childs1,driver=replication,mode=secondary,top-id=childs
> > > + 1
> > > file.file.filename=active_disk.qcow2,\
> > > file.driver=qcow2,\
> > > file.backing.file.filename=hidden_disk.qcow2,\
> > > file.backing.driver=qcow2,\
> > > file.backing.backing=colo1
> > > + -drive if=xxx,driver=quorum,read-pattern=fifo,id=top-disk1,\
> > > + vote-threshold=1,children.0=childs1
> > >
> > > Then run qmp command in secondary qemu:
> > > { 'execute': 'nbd-server-start', @@ -234,6 +240,8 @@ Secondary:
> > > The primary host is down, so we should do the following thing:
> > > { 'execute': 'nbd-server-stop' }
> > >
> > > +Promote Secondary to Primary:
> > > + see COLO-FT.txt
> > > +
> > > TODO:
> > > -1. Continuous block replication
> > > -2. Shared disk
> > > +1. Shared disk
> > > --
> > > 2.20.1
