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Global Cluster Option with two single node cluster?

Created: 24 Jan 2011 • Updated: 25 Jan 2011 | 5 comments
cmoreno1978's picture
This issue has been solved. See solution.

Hi all,

The question is simple, i`m checking the requeriments for this configuration, Cab we configure a global cluster between two single node cluster?

According to the characteristics of the customer platform, the only configuration possible to us is to implement a global cluster that is responsible for monitoring replication groups and fail over applications in case of serious failure in the main site.

I understand that we can configure a single-node cluster but I need  help  to consider any request or cons if we set a global cluster with two single node cluster

Thanks in advance,

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Gaurav Sangamnerkar's picture


Yes, that is very much possible...

From VCS 5.1 admin guide for solaris located at:

Prerequisites for global clusters

This section describes the prerequisites for configuring global clusters.

Cluster setup

You must have at least two clusters to set up a global cluster. Every cluster must
have the required licenses. A cluster can be part of one global cluster. VCS
supports a maximum of four clusters participating in a global cluster.
Clusters must be running on the same platform; the operating system versions
can be different. Clusters must be using the same VCS version.
Cluster names must be unique within each global cluster; system and resource
names need not be unique across clusters. Service group names need not be
unique across clusters; however, global service groups must have identical
Every cluster must have a valid virtual IP address, which is tied to the cluster.
Define this IP address in the cluster’s ClusterAddress attribute. This address is
normally configured as part of the initial VCS installation. The IP address must
have a DNS entry.
The global cluster operations require that the port for Wide-Area Connector
(WAC) process (default is 14155) are open across firewalls.
All clusters in a global cluster must use either IPv4 or IPv6 addresses. VCS does
not support configuring clusters that use different Internet Protocol versions in
a global cluster.
For remote cluster operations, you must configure a VCS user with the same
name and privileges in each cluster.


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mikebounds's picture

You can configure a global cluster with two single node clusters, but you should consider RDC (replicated Data cluster) if your nodes are fairly closed together (less than 50km, but possibly further apart).  You also need to consider what you are trying to provide - most people trying to configure this kind of set-up are trying to provide both HA and DR and this doesn't really work.  A few points on GCO v RDC:

  1. RDC is designed for sites closer together and GCO is designed for sites far apart.
  2. Failover is automatic by default for RDC and manual for GCO (both can be configured for Automatic or Manual failover)
  3. Detection of node failure (so that a failover is invoked) is by default 15 seconds for RDC and 3 – 4 minutes for GCO (both can be tuned for different values, however an RDC heartbeats continuously and GCO only heartbeats periodically, so GCO cannot be tuned to have as low node failure detection times as RDC without compromising the risk of split-brain.

If you want auto failover, then you need to think carefully about split-brain and also the case where replication is async at the time of failover.

So a few questions:

  1. How far apart are your nodes
  2. Are you trying to provide HA or DR (or both)
  3. Are you using VVR or Hardware replication
  4. What mode of replication are you using - hard sync (fail writes if network is down), soft sync (replicate sync, but switch to async if network is down), or async
  5. What is your RPO and RTO
  6. Do you require automatic failover.


UK Symantec Consultant in VCS, GCO, SF, VVR, VxAT on Solaris, AIX, HP-ux, Linux & Windows

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cmoreno1978's picture

Thanks you guys for quick response and help

To answer the question:

1. More than 100 Km

2. DR, through the WAN with a bandwidth of 1 mbps approx. We have clarified to the customer that for HA and Local failover they need for additional hardware

3. VVR

4. Async or maybe Soft sync, wich are the best option considering the bandwith and type of application? ( is a WEB Server that it refers to a database of not more than 50 GB)

5. RTO= 4 hrs

    RPO= 1 hour

6. Yes.

Thanks again and regards,

mikebounds's picture

I am guessing you mean you need "Automated" failover rather than automatic failover.  What I mean is that you should set Global service groups to have Manual failover and if node dies, then you will get an alert to failover.  On accepting the alert, VCS will "automate" the failover.  I would not recommend setting Global service groups to have Auto failover as if at the time of failover you are in async mode (which you could be in even with soft sync), VCS will take over even if VVR is behind.  Also any network issues between the 2 sites could cause split-brain.  With an RTO of 4 hours, automatic failover should not be required.

Whether to go async or soft sync is down to:

  1. Bandwidth - you can use vradvisor to see if your application ever exceeds 1Mbps - this is small, so I am guessing it might
  2. Latency - it can be quite hard to guage to tell what the effect the latency will have on your application, so you can just test soft sync and see how your application handles this - you can switch between async and soft sync on the fly, so it is not a "hard" setting

If your RPO is 1 hour, then async should suffice and if your bandwidth is sufficient, then in you should only be a second or 2 behind.


UK Symantec Consultant in VCS, GCO, SF, VVR, VxAT on Solaris, AIX, HP-ux, Linux & Windows

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cmoreno1978's picture

Just one more question

RDC now is known as Metro DR with Replication?