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Re: [Linux-cluster] Cluster Planning



Scott,



On 4/20/06, Scott Kellogg <skellogg egginc com> wrote:


The only problem you will encounter is that without a SAN you will probably have to sincronize data between the servers if your application stores data on internar discs on the servers....

Yes, this is the issue that seems to have multiple solutions.  I've looked at NFS, DRBD, rysnc, and Unison, but none of these technologies has jumped out at me as the best one.

Correct

Also to use an active-active (same service active on both servers) configuration + loadbalancing you will need more than 2 servers; at least 4 servers, 2 for loadbalancing (1 active/1 backup) and 2 for the critical service active concurently on both servers (no high availability, no failover).

You seem to be referring to LVS.  Right, I can't implement that since I don't have enough hardware.  I think that active-passive will be the way to go.  When the active node dies, the passive node will take over.  The data will only be as fresh as the last synchronization.  

That begs the question of what happens when the active node comes back up ... will the passive node (now active) sync its data to the new active node?  This is where picking a synchronization method becomes vital.

Excellent point here.
That's the problem when you dont have a SAN --> sync!

Let's suppose we have a 2 node on failover.
NodeA active NodeB passive.
NodeA should be in sync with NodeB
If NodeA dies, NodeB takes over
NodeB must then continue to sync its data to NodeA (when it becomes available again)

This a tough job!

About the sync technologies you mentioned:

DRBD
When you will need a special kernel with support for that. Or recompile a new kenel (be careful since Red Hat wont support any modified piece of software you use, specially the kernel)

NFS:
You will need a dedicated server to provide shares, right?

Rsync:
Must have pretty intelligent scripts to garantee what we discussed above, and still not satisfactory

/Filipe

 

/Scott



But if the active-active is for the servers (hardware), which means not the same service on high availability  then; 2 servers doing loadbalancing (1 active/1 backup), 2 servers providing 2 critical services, one actice on node A and the other one active on node B (failover activated)

Well thats my understanding about Red Hat's Cluster Suite... Please correct me if I Am wrong...

Att.
Filipe Miranda


On 4/20/06, Scott Kellogg <skellogg egginc com> wrote:
Hello,

I was wondering if I could get some assistance in setting up a two
node cluster.

We have 2 Dell PowerEdge 850 machines running RHEL4.  Our license for
Cluster Suite is still in purchasing.  The main thing in the Cluster
Suite documentation which confuses me is the use of a SAN.  RHEL4
docs claim that the need for a SAN has been eliminated, but I'm
having trouble find more information.  Most of the docs assume you
are using a SAN. My customer could not afford the SAN, just the servers.

I would like to set up a high-availablity environment.  I understand
that due to the hardware configuration (no SAN, no RAID) that there
are still points of failure.  I'm hoping to set up a simple active-
passive configuration.  We will be running LAMP applications.  If the
primary server cannot deliver services, I'd like to automatically cut
over to the backup.

Ideally, I'd like to set up active-active and load balancing, since
the servers have DRAC4 fence devices for use with STONITH.  However,
since there is no SAN, I'm not sure how data will be mirrored across
the two machines.

Any help is appreciated!

Thank you,
Scott Kellogg

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Att.
---
Filipe T Miranda
RHCE - Red Hat Certified Engineer
OCP8i - Oracle Certified Professional
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--
Scott Kellogg
System Administrator
EG&G Technical Services, Inc.
(812) 854-7077 ext. 236




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