Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.
On 16/03/14 05:08 AM, khaled atteya wrote: > Thank you Digimer very much for your effort & time. > Would you Please see the question below ? :) > > On Fri, Mar 14, 2014 at 4:44 PM, Digimer <lists at alteeve.ca > <mailto:lists at alteeve.ca>> wrote: > > On 14/03/14 05:34 AM, khaled atteya wrote: > > A- In DRBD Users's guide , in explanation of "resource-only" > which one > of fencing policy , they said: > > "If a node becomes a disconnected primary, it tries to fence the > peer's disk. This is done by calling the fence-peer handler. The > handler > is supposed to reach the > other node over alternative communication paths and call 'drbdadm > outdate minor' there." > > My question is : if the handler can't reach the other node for any > reason ,what will happen ? > > > I always use 'resource-and-stonith', which blocks until the fence > action was a success. As for the fence handler, I always pass the > requests up to the cluster manager. To do this, I use 'rhcs_fence' > on Red Hat clusters (cman + rgmanager) or crm-fence-peer.sh on > corosync + pacemaker clusters. > > In either case, the fence action does not try to log into the other > node. Instead, it uses an external device, like IPMI or PDUs, and > forces the node off. > > > B- In active/passive mode , are these directives have effect: > Are these directives "after-sb-0pri , after-sb-1pri , > after-sb-2pri" > have effects in Active/passive mode or only in Active/Active mode ? > If they have effects , what if i don't set them , is their > default value > for each ? > > > It doesn't matter what mode you are in, it matters what happened > during the time that the nodes were split-brained. If both nodes > were secondary during the split-brain, 0pri policy is used. If one > node was Primary and the other remained secondary, 1pri policy is > used. If both nodes were primary, even for a short time, 2pri is used. > > The reason the policy doesn't matter so much is because the roles > matter, not how they got there. For example, if you or someone else > assumed the old primary was dead and manually promoted the > secondary, you have a two-primary split-brain, despite the normal > mode of operation. > > > For the previous section , Are you meaning If i assumed the old primary > was dead and manually promoted the secondary ,split-brain will happen > despite the two nodes can communicate each other ? In other way , would > you please explain this : "if you or someone else assumed the old > primary was dead and manually promoted the secondary, you have a > two-primary split-brain, _despite the normal mode of operation_." , > especially underlined sentence ? Correct. A split brain occurs the moment both nodes are StandAlone and UpToDate. The policy used in recovery depends on whether, at *any* while the nodes are StandAlone/UpToDate, a node went Primary. So if neither node went Primary, 0pri is used. If only one was Primary and the other stayed Secondary, 1pri is used. If both went Primary while being StandAlone/UpToDate, even if for just a moment, 2pri is used. > C- can I use SBD fencing with drbd+pacemaker rather than IPMI or > PDU? > > > No, I do not believe so. The reason being that if the nodes > split-brain, both will think they have access to the "SAN" storage. > Where as with a real (external) SAN, it's possible to say "only one > node is allowed to talk and the other is blocked. There is no way > for one node to block access to the other node's local DRBD data. > > IPMI/PDU fencing is certainly the way to go. > > -- > Digimer > Papers and Projects: https://alteeve.ca/w/ > What if the cure for cancer is trapped in the mind of a person > without access to education? > > > > > -- > KHALED MOHAMMED ATTEYA > System Engineer > > > > _______________________________________________ > drbd-user mailing list > drbd-user at lists.linbit.com > http://lists.linbit.com/mailman/listinfo/drbd-user > -- Digimer Papers and Projects: https://alteeve.ca/w/ What if the cure for cancer is trapped in the mind of a person without access to education?