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) > >>>> "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 ;-) > > That's why I thought "stonith-timeout" might have a role there, as it looks > like a stonith device then... > > By pure tech interest here, some more input or documentation to read about how > it works would be really appreciated. > >> When a block-device is being used it guards the >> communication with the fence-agent communicating with the >> block-device. > OK > > > Thank you for your help! _______________________________________________ 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
