On Wed, 14 Dec 2016 14:52:41 +0100 Klaus Wenninger <kwenn...@redhat.com> 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 <j...@dalibo.com> 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. > >> "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 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! -- Jehan-Guillaume de Rorthais Dalibo _______________________________________________ Users mailing list: Users@clusterlabs.org 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