333 lines
18 KiB
Text
333 lines
18 KiB
Text
COarse-grained LOck-stepping Virtual Machines for Non-stop Service
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----------------------------------------
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Copyright (c) 2016 Intel Corporation
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Copyright (c) 2016 HUAWEI TECHNOLOGIES CO., LTD.
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Copyright (c) 2016 Fujitsu, Corp.
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This work is licensed under the terms of the GNU GPL, version 2 or later.
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See the COPYING file in the top-level directory.
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This document gives an overview of COLO's design and how to use it.
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== Background ==
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Virtual machine (VM) replication is a well known technique for providing
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application-agnostic software-implemented hardware fault tolerance,
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also known as "non-stop service".
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COLO (COarse-grained LOck-stepping) is a high availability solution.
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Both primary VM (PVM) and secondary VM (SVM) run in parallel. They receive the
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same request from client, and generate response in parallel too.
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If the response packets from PVM and SVM are identical, they are released
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immediately. Otherwise, a VM checkpoint (on demand) is conducted.
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== Architecture ==
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The architecture of COLO is shown in the diagram below.
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It consists of a pair of networked physical nodes:
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The primary node running the PVM, and the secondary node running the SVM
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to maintain a valid replica of the PVM.
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PVM and SVM execute in parallel and generate output of response packets for
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client requests according to the application semantics.
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The incoming packets from the client or external network are received by the
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primary node, and then forwarded to the secondary node, so that both the PVM
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and the SVM are stimulated with the same requests.
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COLO receives the outbound packets from both the PVM and SVM and compares them
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before allowing the output to be sent to clients.
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The SVM is qualified as a valid replica of the PVM, as long as it generates
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identical responses to all client requests. Once the differences in the outputs
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are detected between the PVM and SVM, COLO withholds transmission of the
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outbound packets until it has successfully synchronized the PVM state to the SVM.
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Primary Node Secondary Node
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+------------+ +-----------------------+ +------------------------+ +------------+
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| | | HeartBeat +<----->+ HeartBeat | | |
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| Primary VM | +-----------+-----------+ +-----------+------------+ |Secondary VM|
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| | | | | |
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| | +-----------|-----------+ +-----------|------------+ | |
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| | |QEMU +---v----+ | |QEMU +----v---+ | | |
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| | | |Failover| | | |Failover| | | |
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| | | +--------+ | | +--------+ | | |
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| | | +---------------+ | | +---------------+ | | |
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| | | | VM Checkpoint +-------------->+ VM Checkpoint | | | |
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| | | +---------------+ | | +---------------+ | | |
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|Requests<--------------------------\ /-----------------\ /--------------------->Requests|
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| | | ^ ^ | | | | | | |
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|Responses+---------------------\ /-|-|------------\ /-------------------------+Responses|
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| | | | | | | | | | | | | | | |
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| | | +-----------+ | | | | | | | | | | +----------+ | | |
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| | | | COLO disk | | | | | | | | | | | | COLO disk| | | |
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| | | | Manager +---------------------------->| Manager | | | |
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| | | ++----------+ v v | | | | | v v | +---------++ | | |
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| | | |+-----------+-+-+-++| | ++-+--+-+---------+ | | | |
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| | | || COLO Proxy || | | COLO Proxy | | | | |
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| | | || (compare packet || | |(adjust sequence | | | | |
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| | | ||and mirror packet)|| | | and ACK) | | | | |
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| | | |+------------+---+-+| | +-----------------+ | | | |
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+------------+ +-----------------------+ +------------------------+ +------------+
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+------------+ | | | | +------------+
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| VM Monitor | | | | | | VM Monitor |
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+------------+ | | | | +------------+
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+---------------------------------------+ +----------------------------------------+
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| Kernel | | | | | Kernel | |
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+---------------------------------------+ +----------------------------------------+
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| | | |
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+--------------v+ +---------v---+--+ +------------------+ +v-------------+
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| Storage | |External Network| | External Network | | Storage |
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+---------------+ +----------------+ +------------------+ +--------------+
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== Components introduction ==
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You can see there are several components in COLO's diagram of architecture.
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Their functions are described below.
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HeartBeat:
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Runs on both the primary and secondary nodes, to periodically check platform
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availability. When the primary node suffers a hardware fail-stop failure,
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the heartbeat stops responding, the secondary node will trigger a failover
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as soon as it determines the absence.
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COLO disk Manager:
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When primary VM writes data into image, the colo disk manager captures this data
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and sends it to secondary VM's which makes sure the context of secondary VM's
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image is consistent with the context of primary VM 's image.
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For more details, please refer to docs/block-replication.txt.
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Checkpoint/Failover Controller:
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Modifications of save/restore flow to realize continuous migration,
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to make sure the state of VM in Secondary side is always consistent with VM in
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Primary side.
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COLO Proxy:
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Delivers packets to Primary and Secondary, and then compare the responses from
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both side. Then decide whether to start a checkpoint according to some rules.
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Please refer to docs/colo-proxy.txt for more information.
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Note:
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HeartBeat has not been implemented yet, so you need to trigger failover process
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by using 'x-colo-lost-heartbeat' command.
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== COLO operation status ==
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+-----------------+
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| |
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| Start COLO |
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| |
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+--------+--------+
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| Main qmp command:
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| migrate-set-capabilities with x-colo
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| migrate
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v
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+--------+--------+
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| |
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| COLO running |
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| |
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+--------+--------+
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| Main qmp command:
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| x-colo-lost-heartbeat
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| or
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| some error happened
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v
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+--------+--------+
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| | send qmp event:
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| COLO failover | COLO_EXIT
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| |
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+-----------------+
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COLO use the qmp command to switch and report operation status.
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The diagram just shows the main qmp command, you can get the detail
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in test procedure.
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== Test procedure ==
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Note: Here we are running both instances on the same host for testing,
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change the IP Addresses if you want to run it on two hosts. Initially
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127.0.0.1 is the Primary Host and 127.0.0.2 is the Secondary Host.
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== Startup qemu ==
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1. Primary:
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Note: Initially, $imagefolder/primary.qcow2 needs to be copied to all hosts.
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You don't need to change any IP's here, because 0.0.0.0 listens on any
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interface. The chardev's with 127.0.0.1 IP's loopback to the local qemu
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instance.
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# imagefolder="/mnt/vms/colo-test-primary"
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# qemu-system-x86_64 -enable-kvm -cpu qemu64,kvmclock=on -m 512 -smp 1 -qmp stdio \
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-device piix3-usb-uhci -device usb-tablet -name primary \
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-netdev tap,id=hn0,vhost=off,helper=/usr/lib/qemu/qemu-bridge-helper \
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-device rtl8139,id=e0,netdev=hn0 \
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-chardev socket,id=mirror0,host=0.0.0.0,port=9003,server=on,wait=off \
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-chardev socket,id=compare1,host=0.0.0.0,port=9004,server=on,wait=on \
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-chardev socket,id=compare0,host=127.0.0.1,port=9001,server=on,wait=off \
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-chardev socket,id=compare0-0,host=127.0.0.1,port=9001 \
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-chardev socket,id=compare_out,host=127.0.0.1,port=9005,server=on,wait=off \
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-chardev socket,id=compare_out0,host=127.0.0.1,port=9005 \
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-object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0 \
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-object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out \
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-object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0 \
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-object iothread,id=iothread1 \
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-object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,\
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outdev=compare_out0,iothread=iothread1 \
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-drive if=ide,id=colo-disk0,driver=quorum,read-pattern=fifo,vote-threshold=1,\
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children.0.file.filename=$imagefolder/primary.qcow2,children.0.driver=qcow2 -S
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2. Secondary:
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Note: Active and hidden images need to be created only once and the
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size should be the same as primary.qcow2. Again, you don't need to change
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any IP's here, except for the $primary_ip variable.
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# imagefolder="/mnt/vms/colo-test-secondary"
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# primary_ip=127.0.0.1
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# qemu-img create -f qcow2 $imagefolder/secondary-active.qcow2 10G
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# qemu-img create -f qcow2 $imagefolder/secondary-hidden.qcow2 10G
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# qemu-system-x86_64 -enable-kvm -cpu qemu64,kvmclock=on -m 512 -smp 1 -qmp stdio \
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-device piix3-usb-uhci -device usb-tablet -name secondary \
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-netdev tap,id=hn0,vhost=off,helper=/usr/lib/qemu/qemu-bridge-helper \
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-device rtl8139,id=e0,netdev=hn0 \
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-chardev socket,id=red0,host=$primary_ip,port=9003,reconnect=1 \
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-chardev socket,id=red1,host=$primary_ip,port=9004,reconnect=1 \
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-object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0 \
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-object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1 \
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-object filter-rewriter,id=rew0,netdev=hn0,queue=all \
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-drive if=none,id=parent0,file.filename=$imagefolder/primary.qcow2,driver=qcow2 \
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-drive if=none,id=childs0,driver=replication,mode=secondary,file.driver=qcow2,\
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top-id=colo-disk0,file.file.filename=$imagefolder/secondary-active.qcow2,\
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file.backing.driver=qcow2,file.backing.file.filename=$imagefolder/secondary-hidden.qcow2,\
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file.backing.backing=parent0 \
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-drive if=ide,id=colo-disk0,driver=quorum,read-pattern=fifo,vote-threshold=1,\
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children.0=childs0 \
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-incoming tcp:0.0.0.0:9998
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3. On Secondary VM's QEMU monitor, issue command
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{"execute":"qmp_capabilities"}
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{"execute": "nbd-server-start", "arguments": {"addr": {"type": "inet", "data": {"host": "0.0.0.0", "port": "9999"} } } }
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{"execute": "nbd-server-add", "arguments": {"device": "parent0", "writable": true } }
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Note:
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a. The qmp command nbd-server-start and nbd-server-add must be run
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before running the qmp command migrate on primary QEMU
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b. Active disk, hidden disk and nbd target's length should be the
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same.
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c. It is better to put active disk and hidden disk in ramdisk. They
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will be merged into the parent disk on failover.
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4. On Primary VM's QEMU monitor, issue command:
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{"execute":"qmp_capabilities"}
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{"execute": "human-monitor-command", "arguments": {"command-line": "drive_add -n buddy driver=replication,mode=primary,file.driver=nbd,file.host=127.0.0.2,file.port=9999,file.export=parent0,node-name=replication0"}}
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{"execute": "x-blockdev-change", "arguments":{"parent": "colo-disk0", "node": "replication0" } }
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{"execute": "migrate-set-capabilities", "arguments": {"capabilities": [ {"capability": "x-colo", "state": true } ] } }
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{"execute": "migrate", "arguments": {"uri": "tcp:127.0.0.2:9998" } }
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Note:
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a. There should be only one NBD Client for each primary disk.
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b. The qmp command line must be run after running qmp command line in
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secondary qemu.
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5. After the above steps, you will see, whenever you make changes to PVM, SVM will be synced.
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You can issue command '{ "execute": "migrate-set-parameters" , "arguments":{ "x-checkpoint-delay": 2000 } }'
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to change the idle checkpoint period time
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6. Failover test
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You can kill one of the VMs and Failover on the surviving VM:
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If you killed the Secondary, then follow "Primary Failover". After that,
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if you want to resume the replication, follow "Primary resume replication"
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If you killed the Primary, then follow "Secondary Failover". After that,
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if you want to resume the replication, follow "Secondary resume replication"
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== Primary Failover ==
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The Secondary died, resume on the Primary
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{"execute": "x-blockdev-change", "arguments":{ "parent": "colo-disk0", "child": "children.1"} }
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{"execute": "human-monitor-command", "arguments":{ "command-line": "drive_del replication0" } }
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{"execute": "object-del", "arguments":{ "id": "comp0" } }
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{"execute": "object-del", "arguments":{ "id": "iothread1" } }
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{"execute": "object-del", "arguments":{ "id": "m0" } }
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{"execute": "object-del", "arguments":{ "id": "redire0" } }
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{"execute": "object-del", "arguments":{ "id": "redire1" } }
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{"execute": "x-colo-lost-heartbeat" }
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== Secondary Failover ==
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The Primary died, resume on the Secondary and prepare to become the new Primary
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{"execute": "nbd-server-stop"}
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{"execute": "x-colo-lost-heartbeat"}
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{"execute": "object-del", "arguments":{ "id": "f2" } }
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{"execute": "object-del", "arguments":{ "id": "f1" } }
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{"execute": "chardev-remove", "arguments":{ "id": "red1" } }
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{"execute": "chardev-remove", "arguments":{ "id": "red0" } }
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{"execute": "chardev-add", "arguments":{ "id": "mirror0", "backend": {"type": "socket", "data": {"addr": { "type": "inet", "data": { "host": "0.0.0.0", "port": "9003" } }, "server": true } } } }
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{"execute": "chardev-add", "arguments":{ "id": "compare1", "backend": {"type": "socket", "data": {"addr": { "type": "inet", "data": { "host": "0.0.0.0", "port": "9004" } }, "server": true } } } }
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{"execute": "chardev-add", "arguments":{ "id": "compare0", "backend": {"type": "socket", "data": {"addr": { "type": "inet", "data": { "host": "127.0.0.1", "port": "9001" } }, "server": true } } } }
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{"execute": "chardev-add", "arguments":{ "id": "compare0-0", "backend": {"type": "socket", "data": {"addr": { "type": "inet", "data": { "host": "127.0.0.1", "port": "9001" } }, "server": false } } } }
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{"execute": "chardev-add", "arguments":{ "id": "compare_out", "backend": {"type": "socket", "data": {"addr": { "type": "inet", "data": { "host": "127.0.0.1", "port": "9005" } }, "server": true } } } }
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{"execute": "chardev-add", "arguments":{ "id": "compare_out0", "backend": {"type": "socket", "data": {"addr": { "type": "inet", "data": { "host": "127.0.0.1", "port": "9005" } }, "server": false } } } }
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== Primary resume replication ==
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Resume replication after new Secondary is up.
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Start the new Secondary (Steps 2 and 3 above), then on the Primary:
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{"execute": "drive-mirror", "arguments":{ "device": "colo-disk0", "job-id": "resync", "target": "nbd://127.0.0.2:9999/parent0", "mode": "existing", "format": "raw", "sync": "full"} }
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Wait until disk is synced, then:
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{"execute": "stop"}
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{"execute": "block-job-cancel", "arguments":{ "device": "resync"} }
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{"execute": "human-monitor-command", "arguments":{ "command-line": "drive_add -n buddy driver=replication,mode=primary,file.driver=nbd,file.host=127.0.0.2,file.port=9999,file.export=parent0,node-name=replication0"}}
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{"execute": "x-blockdev-change", "arguments":{ "parent": "colo-disk0", "node": "replication0" } }
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{"execute": "object-add", "arguments":{ "qom-type": "filter-mirror", "id": "m0", "netdev": "hn0", "queue": "tx", "outdev": "mirror0" } }
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{"execute": "object-add", "arguments":{ "qom-type": "filter-redirector", "id": "redire0", "netdev": "hn0", "queue": "rx", "indev": "compare_out" } }
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{"execute": "object-add", "arguments":{ "qom-type": "filter-redirector", "id": "redire1", "netdev": "hn0", "queue": "rx", "outdev": "compare0" } }
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{"execute": "object-add", "arguments":{ "qom-type": "iothread", "id": "iothread1" } }
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{"execute": "object-add", "arguments":{ "qom-type": "colo-compare", "id": "comp0", "primary_in": "compare0-0", "secondary_in": "compare1", "outdev": "compare_out0", "iothread": "iothread1" } }
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{"execute": "migrate-set-capabilities", "arguments":{ "capabilities": [ {"capability": "x-colo", "state": true } ] } }
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{"execute": "migrate", "arguments":{ "uri": "tcp:127.0.0.2:9998" } }
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Note:
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If this Primary previously was a Secondary, then we need to insert the
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filters before the filter-rewriter by using the
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""insert": "before", "position": "id=rew0"" Options. See below.
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== Secondary resume replication ==
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Become Primary and resume replication after new Secondary is up. Note
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that now 127.0.0.1 is the Secondary and 127.0.0.2 is the Primary.
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Start the new Secondary (Steps 2 and 3 above, but with primary_ip=127.0.0.2),
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then on the old Secondary:
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{"execute": "drive-mirror", "arguments":{ "device": "colo-disk0", "job-id": "resync", "target": "nbd://127.0.0.1:9999/parent0", "mode": "existing", "format": "raw", "sync": "full"} }
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Wait until disk is synced, then:
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{"execute": "stop"}
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{"execute": "block-job-cancel", "arguments":{ "device": "resync" } }
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{"execute": "human-monitor-command", "arguments":{ "command-line": "drive_add -n buddy driver=replication,mode=primary,file.driver=nbd,file.host=127.0.0.1,file.port=9999,file.export=parent0,node-name=replication0"}}
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{"execute": "x-blockdev-change", "arguments":{ "parent": "colo-disk0", "node": "replication0" } }
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{"execute": "object-add", "arguments":{ "qom-type": "filter-mirror", "id": "m0", "insert": "before", "position": "id=rew0", "netdev": "hn0", "queue": "tx", "outdev": "mirror0" } }
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{"execute": "object-add", "arguments":{ "qom-type": "filter-redirector", "id": "redire0", "insert": "before", "position": "id=rew0", "netdev": "hn0", "queue": "rx", "indev": "compare_out" } }
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{"execute": "object-add", "arguments":{ "qom-type": "filter-redirector", "id": "redire1", "insert": "before", "position": "id=rew0", "netdev": "hn0", "queue": "rx", "outdev": "compare0" } }
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{"execute": "object-add", "arguments":{ "qom-type": "iothread", "id": "iothread1" } }
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{"execute": "object-add", "arguments":{ "qom-type": "colo-compare", "id": "comp0", "primary_in": "compare0-0", "secondary_in": "compare1", "outdev": "compare_out0", "iothread": "iothread1" } }
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{"execute": "migrate-set-capabilities", "arguments":{ "capabilities": [ {"capability": "x-colo", "state": true } ] } }
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{"execute": "migrate", "arguments":{ "uri": "tcp:127.0.0.1:9998" } }
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== TODO ==
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1. Support shared storage.
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2. Develop the heartbeat part.
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3. Reduce checkpoint VM’s downtime while doing checkpoint.
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