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.
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?
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