Eric Kerin wrote:
Janne Peltonen wrote:
On Tue, Nov 21, 2006 at 08:26:20AM -0500, Eric Kerin wrote:
So to keep that scenario from happening, the cluster software
ensures that a successful fence occurs before continuing operation.
It's a fail-safe style setup. Better to take 30 minutes downtime for
an admin to make the right decision than corrupt your filesystems
and have to take 8 -24 hours downtime to restore the system.
I do understand the basics. I wouldn't want the cluster suite to think
that a node couldn't access a resource such as an FS when it can. It
would just be nice to configure the cluster suite so that if one method
of fencing fails, it tries another, <SNIP>
Actually, that's entirely possible.
See: http://sources.redhat.com/cluster/faq.html#fence_levels
And here's an example block from the cluster.conf file first it tries
ilo (HP Lights Out), and if that fails, apc (APC Network power
controller) (the ILO sections is probably not correct, I just thew it
in there as an example of how you'd setup the method tags):
This is correct -- but I wanted to take this chance to provide some
additional information on the configuration that you present.
<fence>
<method name="ilo">
The method name can be anything here - it really does not correspond to
anything else in the file...it could just as easily be name="1" and
name="2"...as long as the method names are unique beneath any
clusternode. system-config-cluster uses "1", "2", "3",etc...
<device name="server1-ilo"
option="off"/>
<device name="server1-ilo"
option="on"/>
It is usually not necessary to specify options for off and on.....the
default for every fence agent is off, then on.
</method>
<method name="apc">
<device name="APC01a" port="1"
option="off"/>
<device name="APC01b" port="1"
option="off"/>
<device name="APC01a" port="1"
option="on"/>
<device name="APC01b" port="1"
option="on"/>
Now here is a case where it IS necessary to specify options...this
configuration is usually used for nodes with dual power supplies to
insure that both power supplies are powered off, before one of them is
powered on. If you use system-config-cluster for configuration, there is
no way to set options, BUT: If you are using power fencing and there are
multiple power fence device tags inside a method block, then the
configuration written out by system-config-cluster looks like the one
above; the option fields are written for you and the ordering of the
devices is set up to insure all power type fences are powered off, and
then all are powered on. The new management interface will also set this
up for you.
Regards,
-Jim
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