Integrate HA Service Guard without Storage

[Arun Jain]

Hi all,

I have to integrate HA Service guard on a 2 node cluster but storage is available right now.

Is it possible in this manner to configure the cluster and add storage afterwards.

If no then please share some authentic document to support the answer.

Thanks in Advance
Arun Jain

[Arun Jain]

Hi All,

Please correct the above line. Storage is not available right now.

[Michal Kapalka (mikap)]

hi,

i would recomend you too look at this docu :

http://docs.hp.com/en/B3936-90100/index.html

and an example installation guide :

http://thomasvogt.wordpress.com/2008/08/26/mcserviceguard-cluster-installation-on-hp-ux-1131/

- i think you need to have a LOCK-DISK ( shared storage ) or QUORUM server.

mikap

[S.N.S]

Hi Arun,

Simply put - the SG is to overcome any SINGLE point of failure.

Now the shared storage, SAN, has the application configured for high avaliability - redundant paths, RAID level protection, FC switches..

In the event of the application (or package in SG terms) runs on a HPUX node, simply the faiure of THIS node means the failure of the application itself => NO High Avaliability

Inshort, the purpose of HA isnt met if the storage isnt there..( though, you can setup a partial Cluster for testing using NFS, but for learning only)

The rest you can read from the docs above.


HTH
SNS

Points for all those who have been of resonable help :-) !

[Arun Jain]

Hi S.N.S and Michael,

You mean to say that in the event of Installing HA, we cannot integrate a cluster in absence of storage and cannot create a environment where we plug in a storage afterwards and our cluster works.

Regards
Arun Jain

[S-M-S]

Hi Arun,
You will be needing a storage space(lUN') which is visible to both node for creating a 2 node cluster

Thanks,
SMS

[R.O.]

I have created several "single node" pakageless clusters, with the sole purpose of having lan high availability. Yo can do it and later, add a second node and shared storage

[Michal Kapalka (mikap)]

R.O,

i can only confirm this, single node HA solution is mostly using for NETOWRKING,
because it will replace the APA.

I saw it many time on the customer servers.

On the 11iv3 its doesn't mater because the APA is included in the VSE-OE / HA-OE.


PS : "Arun Jain" need to use 2 node cluster enviroment.

mikap

[S-M-S]

Arun,
You can go ahead with the 2 node cluster configuration before geting the storagespace for data.

In this case you need a shared lockdisk( 100 - 1000 mb will work) for vglock. Thats what required from SAN

[Michal Kapalka (mikap)]

hi,

#==============================================
In this case you need a shared lockdisk( 100 - 1000 mb will work) for vglock. Thats what required from SAN
#==============================================

or creating of a QUORUM server, instead of LOCK DISK.

mikap

[Arun Jain]

Hi S.M.S,

Thanks for the feedback, but the problem here is, I dont have SAN env with me.

I just need to confirm that without SAN, can we go for HA integration and after that plug in the storage and no new configuration is to be done.

Regards
Arun

[Michal Kapalka (mikap)]

Hi Arun,

thats not possible, because if the servisguard will take care of shared storage, activation of VG-s, you need to reconfigure the cluster.

So you should be able to configure cluster,

IP / VIP / HA IP ..... but if you like to test the config you should have the storage and file system hierarchy created before.

mikap

[R.O.]

From the official document "Managing Serviceguard Version A.11.16, B3936-90079"


"If you have a two-node cluster, you are required to configure a cluster
lock. If communications are lost between these two nodes, the node that
obtains the cluster lock will take over the cluster and the other node will
halt or perform a TOC. Without a cluster lock, a failure of either node in
the cluster will cause the other node, and therefore the cluster, to halt.
Note also that if the cluster lock fails during an attempt to acquire it, the
cluster will halt."

On the other hand:

"Use of the Quorum Server as the Cluster Lock
A quorum server can be used in clusters of any size. The quorum server
process runs on a machine outside of the cluster for which it is providing
quorum services. The quorum server listens to connection requests from
the Serviceguard nodes on a known port. The server maintains a special
area in memory for each cluster, and when a node obtains the cluster
lock, this area is marked so that other nodes will recognize the lock as
â taken.â If communications are lost between two equal-sized groups of
nodes, the group that obtains the lock from the Quorum Server will take
over the cluster and the other nodes will perform a TOC. Without a
cluster lock, a failure of either group of nodes will cause the other group,
and therefore the cluster, to halt. Note also that if the quorum server is
not available during an attempt to access it, the cluster will halt."

So you can create a two node's cluster without shared storage by using instead a quorum server.

Regards,

[S.N.S]

RO,

That section pertains to ONLY the Cluster lock that can be a LUN/Disk or the Quorum Server -the lock is for cluster node arbitration is case of node failure- preventing the so-called split-brain syndrome : wherein multiple nodes try to start the cluster

If not the SAN, where would you run the packages? you certainly can't do it on any of the servers - defeats the whole purpose

Correct me if I am mistaken - folks

HTH
SNS

[R.O.]

SNS,

Yes you are right, but I think a two nodes cluster with a quorum server can be created BUT without packages.... Is it useful? I don't think so, but in theory it is possible to configure in this way. Please, correct me if I am wrong.

Regards,

[S.N.S]

Yes, RO - the quorum server is any server; and used for Clusters with more than 4nodes.
So the Cluster Lock - here the quorum server - is not on the SAN..
For applications/packages to run - we need the shared storage SAN >>> as per my understanding :-)

Cheers!
SNS

[Stephen Doud]

You can create a 2-node cluster using a Quorum server as a cluster arbitration device.

If you don't have the shared storage capability yet, why build a cluster? A cluster without an array would only provide standby LAN failover. APA could provide a similar function without the additional complexity.

[Serviceguard for Linux]

Not to totally disagree with Stephen:

Simply put, if you care that the data written to storage by an application running on one NODE1 be available to the application running on NODE2 after failover, then wait until your shared storage is available. In this case, you only have a learning opportunity.

If, however, there is no need for that data availability, then you can build a useful cluster with no shared storage as long as you have a Quorum Server.

Note: The number of customers I am aware of that have deployed clusters with no shared storage can probably be counted on one hand.

[S.N.S]

Thanks Stephen, SGLX for that bit...Arun, I guess you have been answered :-)

SNS