[ClusterLabs] Questions about SBD behavior

Klaus Wenninger kwenning at redhat.com
Fri May 25 03:08:23 EDT 2018


On 05/25/2018 07:31 AM, 井上 和徳 wrote:
> Hi,
>
> I am checking the watchdog function of SBD (without shared block-device).
> In a two-node cluster, if one cluster is stopped, watchdog is triggered on the remaining node.
> Is this the designed behavior?

SBD without a shared block-device doesn't really make sense on
a two-node cluster.
The basic idea is - e.g. in a case of a networking problem -
that a cluster splits up in a quorate and a non-quorate partition.
The quorate partition stays over while SBD guarantees a
reliable watchdog-based self-fencing of the non-quorate partition
within a defined timeout.
This idea of course doesn't work with just 2 nodes.
Taking quorum info from the 2-node feature of corosync (automatically
switching on wait-for-all) doesn't help in this case but instead
would lead to split-brain.
What you can do - and what e.g. pcs does automatically - is enable
the auto-tie-breaker instead of two-node in corosync. But that
still doesn't give you a higher availability than the one of the
winner of auto-tie-breaker. (Maybe interesting if you are going
for a load-balancing-scenario that doesn't affect availability or
for a transient state while setting up a cluste node-by-node ...)
What you can do though is using qdevice to still have 'real-quorum'
info with just 2 full cluster-nodes.

There was quite a lot of discussion round this topic on this
thread previously if you search the history.

Regards,
Klaus

>
> [vmrh75b]# cat /etc/corosync/corosync.conf
> (snip)
> quorum {
>     provider: corosync_votequorum
>     two_node: 1
> }
>
> [vmrh75b]# cat /etc/sysconfig/sbd
> # This file has been generated by pcs.
> SBD_DELAY_START=no
> ## SBD_DEVICE="/dev/vdb1"
> SBD_OPTS="-vvv"
> SBD_PACEMAKER=yes
> SBD_STARTMODE=always
> SBD_WATCHDOG_DEV=/dev/watchdog
> SBD_WATCHDOG_TIMEOUT=5
>
> [vmrh75b]# crm_mon -r1
> Stack: corosync
> Current DC: vmrh75a (version 2.0.0-0.1.rc4.el7-2.0.0-rc4) - partition with quorum
> Last updated: Fri May 25 13:36:07 2018
> Last change: Fri May 25 13:35:22 2018 by root via cibadmin on vmrh75a
>
> 2 nodes configured
> 0 resources configured
>
> Online: [ vmrh75a vmrh75b ]
>
> No resources
>
> [vmrh75b]# pcs property show
> Cluster Properties:
>  cluster-infrastructure: corosync
>  cluster-name: my_cluster
>  dc-version: 2.0.0-0.1.rc4.el7-2.0.0-rc4
>  have-watchdog: true
>  stonith-enabled: false
>
> [vmrh75b]# ps -ef | egrep "sbd|coro|pace"
> root      2169     1  0 13:34 ?        00:00:00 sbd: inquisitor
> root      2170  2169  0 13:34 ?        00:00:00 sbd: watcher: Pacemaker
> root      2171  2169  0 13:34 ?        00:00:00 sbd: watcher: Cluster
> root      2172     1  0 13:34 ?        00:00:00 corosync
> root      2179     1  0 13:34 ?        00:00:00 /usr/sbin/pacemakerd -f
> haclust+  2180  2179  0 13:34 ?        00:00:00 /usr/libexec/pacemaker/pacemaker-based
> root      2181  2179  0 13:34 ?        00:00:00 /usr/libexec/pacemaker/pacemaker-fenced
> root      2182  2179  0 13:34 ?        00:00:00 /usr/libexec/pacemaker/pacemaker-execd
> haclust+  2183  2179  0 13:34 ?        00:00:00 /usr/libexec/pacemaker/pacemaker-attrd
> haclust+  2184  2179  0 13:34 ?        00:00:00 /usr/libexec/pacemaker/pacemaker-schedulerd
> haclust+  2185  2179  0 13:34 ?        00:00:00 /usr/libexec/pacemaker/pacemaker-controld
>
> [vmrh75b]# pcs cluster stop vmrh75a
> vmrh75a: Stopping Cluster (pacemaker)...
> vmrh75a: Stopping Cluster (corosync)...
>
> [vmrh75b]# tail -F /var/log/messages
> May 25 13:37:00 vmrh75b pacemaker-controld[2185]: notice: Our peer on the DC (vmrh75a) is dead
> May 25 13:37:00 vmrh75b pacemaker-controld[2185]: notice: State transition S_NOT_DC -> S_ELECTION
> May 25 13:37:00 vmrh75b pacemaker-controld[2185]: notice: State transition S_ELECTION -> S_INTEGRATION
> May 25 13:37:00 vmrh75b pacemaker-attrd[2183]: notice: Node vmrh75a state is now lost
> May 25 13:37:00 vmrh75b pacemaker-attrd[2183]: notice: Removing all vmrh75a attributes for peer loss
> May 25 13:37:00 vmrh75b pacemaker-attrd[2183]: notice: Lost attribute writer vmrh75a
> May 25 13:37:00 vmrh75b pacemaker-attrd[2183]: notice: Purged 1 peer with id=1 and/or uname=vmrh75a from the membership cache
> May 25 13:37:00 vmrh75b pacemaker-fenced[2181]: notice: Node vmrh75a state is now lost
> May 25 13:37:00 vmrh75b pacemaker-fenced[2181]: notice: Purged 1 peer with id=1 and/or uname=vmrh75a from the membership cache
> May 25 13:37:00 vmrh75b pacemaker-based[2180]: notice: Node vmrh75a state is now lost
> May 25 13:37:00 vmrh75b pacemaker-based[2180]: notice: Purged 1 peer with id=1 and/or uname=vmrh75a from the membership cache
> May 25 13:37:00 vmrh75b pacemaker-controld[2185]: warning: Input I_ELECTION_DC received in state S_INTEGRATION from do_election_check
> May 25 13:37:01 vmrh75b sbd[2171]:   cluster:  warning: set_servant_health: Connected to corosync but requires both nodes present
> May 25 13:37:01 vmrh75b sbd[2171]:   cluster:  warning: notify_parent: Notifying parent: UNHEALTHY (6)
> May 25 13:37:01 vmrh75b sbd[2169]: warning: inquisitor_child: cluster health check: UNHEALTHY
> May 25 13:37:01 vmrh75b sbd[2169]: warning: inquisitor_child: Servant cluster is outdated (age: 226)
> May 25 13:37:01 vmrh75b sbd[2170]:      pcmk:   notice: unpack_config: Watchdog will be used via SBD if fencing is required
> May 25 13:37:01 vmrh75b sbd[2170]:      pcmk:     info: determine_online_status: Node vmrh75b is online
> May 25 13:37:01 vmrh75b sbd[2170]:      pcmk:     info: unpack_node_loop: Node 2 is already processed
> May 25 13:37:01 vmrh75b sbd[2170]:      pcmk:     info: unpack_node_loop: Node 2 is already processed
> May 25 13:37:01 vmrh75b sbd[2171]:   cluster:  warning: notify_parent: Notifying parent: UNHEALTHY (6)
> May 25 13:37:01 vmrh75b corosync[2172]: [TOTEM ] A new membership (192.168.28.132:5712) was formed. Members left: 1
> May 25 13:37:01 vmrh75b corosync[2172]: [QUORUM] Members[1]: 2
> May 25 13:37:01 vmrh75b corosync[2172]: [MAIN  ] Completed service synchronization, ready to provide service.
> May 25 13:37:01 vmrh75b pacemakerd[2179]: notice: Node vmrh75a state is now lost
> May 25 13:37:01 vmrh75b pacemaker-controld[2185]: notice: Node vmrh75a state is now lost
> May 25 13:37:01 vmrh75b pacemaker-controld[2185]: warning: Stonith/shutdown of node vmrh75a was not expected
> May 25 13:37:02 vmrh75b sbd[2171]:   cluster:  warning: notify_parent: Notifying parent: UNHEALTHY (6)
> May 25 13:37:02 vmrh75b pacemaker-schedulerd[2184]: notice: Watchdog will be used via SBD if fencing is required
> May 25 13:37:02 vmrh75b pacemaker-schedulerd[2184]: warning: Blind faith: not fencing unseen nodes
> May 25 13:37:02 vmrh75b pacemaker-schedulerd[2184]: notice: Delaying fencing operations until there are resources to manage
> May 25 13:37:02 vmrh75b pacemaker-schedulerd[2184]: notice: Calculated transition 0, saving inputs in /var/lib/pacemaker/pengine/pe-input-1410.bz2
> May 25 13:37:02 vmrh75b pacemaker-controld[2185]: notice: Transition 0 (Complete=0, Pending=0, Fired=0, Skipped=0, Incomplete=0, Source=/var/lib/pacemaker/pengine/pe-input-1410.bz2): Complete
> May 25 13:37:02 vmrh75b pacemaker-controld[2185]: notice: State transition S_TRANSITION_ENGINE -> S_IDLE
> May 25 13:37:03 vmrh75b sbd[2171]:   cluster:  warning: notify_parent: Notifying parent: UNHEALTHY (6)
> May 25 13:37:03 vmrh75b sbd[2170]:      pcmk:   notice: unpack_config: Watchdog will be used via SBD if fencing is required
> May 25 13:37:03 vmrh75b sbd[2170]:      pcmk:     info: determine_online_status: Node vmrh75b is online
> May 25 13:37:03 vmrh75b sbd[2170]:      pcmk:     info: unpack_node_loop: Node 2 is already processed
> May 25 13:37:03 vmrh75b sbd[2170]:      pcmk:     info: unpack_node_loop: Node 2 is already processed
> May 25 13:37:04 vmrh75b sbd[2171]:   cluster:  warning: notify_parent: Notifying parent: UNHEALTHY (6)
> May 25 13:37:05 vmrh75b sbd[2169]: warning: inquisitor_child: Latency: No liveness for 4 s exceeds threshold of 3 s (healthy servants: 0)
> May 25 13:37:05 vmrh75b sbd[2171]:   cluster:  warning: notify_parent: Notifying parent: UNHEALTHY (6)
> May 25 13:37:05 vmrh75b sbd[2169]: warning: inquisitor_child: Latency: No liveness for 4 s exceeds threshold of 3 s (healthy servants: 0)
>
> Best Regards,
> Kazunori INOUE
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