On Mon, 19 Dec 2016 13:37:09 +0100 Klaus Wenninger <[email protected]> wrote:
> On 12/17/2016 11:55 PM, Jehan-Guillaume de Rorthais wrote: > > On Wed, 14 Dec 2016 14:52:41 +0100 > > Klaus Wenninger <[email protected]> wrote: > > > >> On 12/14/2016 01:26 PM, Jehan-Guillaume de Rorthais wrote: > >>> On Thu, 8 Dec 2016 11:47:20 +0100 > >>> Jehan-Guillaume de Rorthais <[email protected]> wrote: > >>> > >>>> Hello, > >>>> > >>>> While setting this various parameters, I couldn't find documentation and > >>>> details about them. Bellow some questions. > >>>> > >>>> Considering the watchdog module used on a server is set up with a 30s > >>>> timer (lets call it the wdt, the "watchdog timer"), how should > >>>> "SBD_WATCHDOG_TIMEOUT", "stonith-timeout" and "stonith-watchdog-timeout" > >>>> be set? > >>>> > >>>> Here is my thinking so far: > >>>> > >>>> "SBD_WATCHDOG_TIMEOUT < wdt". The sbd daemon should reset the timer > >>>> before the wdt expire so the server stay alive. Online resources and > >>>> default values are usually "SBD_WATCHDOG_TIMEOUT=5s" and "wdt=30s". But > >>>> what if sbd fails to reset the timer multiple times (eg. because of > >>>> excessive load, swap storm etc)? The server will not reset before > >>>> random*SBD_WATCHDOG_TIMEOUT or wdt, right? > >> SBD_WATCHDOG_TIMEOUT (e.g. in /etc/sysconfig/sbd) is already the > >> timeout the hardware watchdog is configured to by sbd-daemon. > > Oh, ok, I did not realized sbd was actually setting the hardware watchdog > > timeout itself based on this variable. After some quick search to make sure > > I understand it right, I suppose it is done there? > > https://github.com/ClusterLabs/sbd/blob/172dcd03eaf26503a10a18501aa1b9f30eed7ee2/src/sbd-common.c#L123 > > > >> sbd-daemon is triggering faster - timeout_loop defaults to 1s but > >> is configurable. > >> > >> SBD_WATCHDOG_TIMEOUT (and maybe the loop timeout as well > >> but significantly shorter should be sufficient) > >> has to be configured so that failing to trigger within time means > >> a failure with high enough certainty or the machine showing > >> comparable response-times would anyway violate timing requirements > >> of the services running on itself and in the cluster. > > OK. So I understand now why 5s is fine as a default value then. > > > >> Have in mind that sbd-daemon defaults to running realtime-scheduled > >> and thus is gonna be more responsive than the usual services > >> on the system. Although you of course have to consider that > >> the watchers (child-processes of sbd that are observing e.g. > >> the block-device(s), corosync, pacemaker_remoted or > >> pacemaker node-health) might be significantly less responsive > >> due to their communication partners. > > I'm not sure yet to understand clearly the mechanism and interactions of sbd > > with other daemons. So far, I understood that Pacemaker/stonithd was able to > > poke sbd to ask it to trigger a node reset through the wd device. I'm very > > new to this area and I still lake of self documentation. > > Pacemaker is setting the node unclean which pacemaker-watcher > (one of sbd daemons) sees as it is connected to the cib. > This is why the mechanism is working (sort of - see the discussion > in my pull request in the sbd-repo) on nodes without stonithd as > well (remote-nodes). > If you are running sbd with a block-device there is of course this > way of communication as well between pacemaker and sbd. > (e.g. via fence_sbd fence-agent) > Be aware that there are different levels of support for these > features in the distributions. (RHEL more on the watchdog-side, > SLES more on the block-device side ... roughly as far as I got it) OK, I have a better understanding of the need for various sbd watchers and how it all sounds to works. > >>>> "stonith-watchdog-timeout > SBD_WATCHDOG_TIMEOUT". I'm not quite sure > >>>> what is stonith-watchdog-timeout. Is it the maximum time to wait from > >>>> stonithd after it asked for a node fencing before it considers the > >>>> watchdog was actually triggered and the node reseted, even with no > >>>> confirmation? I suppose "stonith-watchdog-timeout" is mostly useful to > >>>> stonithd, right? > >> Yes, the time we can assume a node to be killed by the hardware-watchdog... > >> Double the hardware-watchdog-timeout is a good choice. > > OK, thank you > > > >>>> "stonith-watchdog-timeout < stonith-timeout". I understand the stonith > >>>> action timeout should be at least greater than the wdt so stonithd will > >>>> not raise a timeout before the wdt had a chance to exprire and reset the > >>>> node. Is it right? > >> stonith-timeout is the cluster-wide-defaut to wait for stonith-devices > >> to carry out their duty. In the sbd-case without a block-device (sbd used > >> for pacemaker to be observed by a hardware-watchdog) it shouldn't > >> play a role. > > I thought self-fencing through sbd/wd was carried by stonithd because of > > such messages in my PoC log files: > > > > stonith-ng: notice: unpack_config: Relying on watchdog integration for > > fencing > > see above ... or read as sit still and wait for the watchdog to do the > job ;-) Ok, perfectly clear now :) Thank you again! _______________________________________________ Users mailing list: [email protected] http://lists.clusterlabs.org/mailman/listinfo/users Project Home: http://www.clusterlabs.org Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf Bugs: http://bugs.clusterlabs.org
