hosts in a cluster

[thmadd]

Is there a recommended maximum for the number of hosts that should be in a HA DRS cluster? Is there a benefit for breaking up the cluster sizes. We have approx 30 hosts, all sitting 1 HA DRS cluster, and someone posed the question if there would be a benefit by smaller clusters... Any thoughts, Ideas would be appreciated.

[msemon1 · Accepted solution]

You might break up your hosts into some logical clusters. We have a cluster for production hosts, testing and development hosts, and email hosts. Sometimes it makes sense for licensing also. Before we migrated from Lotus Notes we moved all of the Domino Servers into their own cluster because they were licensed based on all of the potential CPU's they could reside on. The can get very expensive in a large cluster! I think the maximum number of hosts per cluster for 3.5 U4 is 32.

Mike

[NWhiley]

It is worth checking that you are not trying to run stuff like HA in an environment where HA itself could fail.

Such as more than 4 nodes in the same chassis if you are on Blades.

See here for detail

http://www.yellow-bricks.com/vmware-high-availability-deepdiv/

Also, I think it is worth keeping clusters to a minimum, if you can split 32 hosts into two logical 16 host clusters, I'd go for that.

It leaves you room to grow and splits out systems.

VCP

[msemon1]

I have 16 hosts split into 3 clusters

3 Testing and Development

3 Email

11 Production

We do have HA and DRS enabled with number of host failures the cluster can tolerate is 1.

This makes HA and DRS calculations much simpler and more reliable.

MIke

[Ryan2]

Configuration maximum for an HA / DRS cluster is still 32 in vSphere 4. As mentioned, it really depends on what the environment is for. Breaking up Production, Development, Server, Desktop, etc. clusters can help to keep systems in check if you've got several requirements for your VM farm...

[haif]

Hi,

we have a production cluster with 18 esx hosts running on VI3.5u3. Because we get some problems with vmotion, storage vmotion, committing snapshots, and so on, we did a vmware health check.

One result of this was to redesign the infrastructure and create building blocks of max 8 esx hosts per HA/DRS cluster. One reason therefor is that you can configure HA only for a failure of 4 hosts, because HA has 5 primary HA agents and one primary is required to run in the cluster.

We have divided our esx host in 2 seperated server rooms in different buildings. When loosing power or get another problem in one server room, we lost half of our esx environment. When having Clusters bigger than 8 hosts so HA is not able to restart the VMs because more than 4 Hosts failed.

Another reason is to reduce the SCSI reservations on the ESX hosts. When creating smaller building blocks with max 8 hosts, then you can present only the LUNs to each cluster which are needed by the VMs. So you can reduce the number of ESX Hosts which share one LUN. This should reduce SCSI reservations.

-

---

Patrick Häfner

VCP on VI3, vExpert 2009

VMUG Leader Germany South

[Texiwill]

Hello,

While the MAX is 32 hosts per cluster, the real number depends on the workloads specifically those related to disk IO. Your SAN may not be able to handle more than 8 nodes per LUN before it starts to have problems. This has always been the achilles heel of VMware clusters. THe number of nodes per LUN the SAN can handle. LArge SANs generally have no problems but mid and small SANs can.

Best regards,

Edward L. Haletky VMware Communities User Moderator, VMware vExpert 2009, Virtualization Practice Analyst[/url]
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