[Linux-HA] Three or more nodes with Linux-HA
alanr at unix.sh
Tue Aug 16 10:01:31 MDT 2005
Dominique Chabord wrote:
> Hi Alan and Alex,
> Le 11 août 05, à 07:17, Alan Robertson a écrit :
>> Alexander Litvak wrote:
>>> Thanks for the answer. Unfortunately my question was not about how
>>> to go to 2.0 with two node. Site gives plenty of examples for that.
>>> But some people claim that 4, 8, 16 nodes clusters were run. I
>>> wanted to see an example of configuration and applications that could
>>> benefit from that. I don't see anybody explaining how all things
>>> would work in this case at least from 10,000 feet view.
>> Well... you have to have more than two services :-)
> If I run two critical services and I have three servers, is it possible
> to setup heartbeat so that, if two servers are simultaneously down,
> whichever they are, the services are both run on the third computer ?
If you disable quorum, yes. Otherwise, you have to have a clear
majority of the servers running (standard quorum stuff).
>> Or you have to have an n+1 standby node.
> Do you mean that, for every critical service, there are one master and
> one backup preconfigured ?
> Thank you for any comment on these particular points and for all
> heartbeat development.
The method of selecting a node to run a resource on is _extremely_ flexible.
You can basically tell us what criteria you want met by your
configuration and we'll try and meet it.
You can say these kinds of things:
I don't care where this service runs
The service must run on one of these nodes...
I must run it on a node with a fiber channel card
(you have to tell us which nodes have fiber channel cards)
I would rather run it on a node with at least 2 Gig of RAM
(you currently have to tell us how much RAM each node has)
I must run it on the same node as service X
I must not run it on the one service X is running on
I would rather not run it on the same node as service X
I would rather run it on the same node as service X
For any of the "rather" types of requests, you can give relative
weights. Giving it a +INFINITY weight means "must". Giving it a
-INFINITY weight means "must not"
There is a good bit of not-terribly-well-organized documentation on the
web site. There also some papers and talks on this. Barring some
errors in XML comments (which only work in CVS anyway), there is a
sort-of good sized worked sample in an attachment on the Talks page for
a workshop I just completed at LinuxWorld in San Francisco.
Alan Robertson <alanr at unix.sh>
"Openness is the foundation and preservative of friendship... Let me
claim from you at all times your undisguised opinions." - William
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