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 <[email protected]
<mailto:[email protected]>> 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
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--
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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