Enthusiast
Enthusiast

VSAN 2 node robo questions

Hi

We are about to purchase a VSAN ROBO setup from a trusted reseller which costs of a two host setup in a hybrid solution with a witness VM. The plan is to create a new cluster for these 2 nodes solely for the purpose we need these for and this will sit in our existing vCentre environment at Production. The witness VM will sit on another cluster in the same Data Centre. 

At the moment we are still running v6.0 of vCentre which is Windows based but expect to be running the latest supported release of 6.5 at the point of install but running under a VCSA configuration instead. I believe we need to do this to allow us the use of ROBO functionality which is a feature in 6.5.

We just had a few questions which I am hoping might be answered on this forum.

Whilst the configuration we are purchasing is not a VSAN ready node the partner has assisted us with ensuring the hardware components are on the VMware compability list. In each node we will have 1 x 400GB cache and 2 x 600GB capacity tier disks. How much usable capacity would this give us after the creation of 1 VSAN Data store with the disks from the 2 hosts?  If we expand in the future is it just a simple case of adding disks into both hosts and expanding the data store?

With the witness VM which runs ESXi. The licensing key for this would be the same key that will be used to license the 2 physical hosts? Is that correct or is there a specific license key for the witness VM? If this needs a separate license key would I need to ask the partner to supply this as part of their costings?

In addition to the witness VM, as our other cluster will utilise other ESXi nodes, these nodes don’t have any storage as ESXi is booted via a SD card and the VM storage is served through our current 3rd party SAN storage. The witness states it needs a cache and capacity tier, we don’t have any SSD in the environment but I believe for the witness you don’t need SSD. Would this be correct?  

Due to cost we decided not to purchase the 25 VM ROBO license but instead puchased vSphere standard and VSAN 6 standard as separate products, I assume we won’t have the issue with the VSAN for ROBO licensing which is limited to 25 VMs, would that be correct? It’s unlikely this environment will ever grow more than 6 VMs in the future. The licensing we are purchasing now will allow us to have up to a maximum of VMs for the whole cluster.

Any points on this questions would be greatly appreciated.


Thanks

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6 Replies
VMware Employee
VMware Employee

Hello ictadminrbassi

"I believe we need to do this to allow us the use of ROBO functionality which is a feature in 6.5."

ROBO has existed since 6.0 (6.1), 'ROBO' as a 2-node cluster not using ROBO-25pack licensing is possible, are you setting this up as a 2-Node Direct Connect? - This is 6.5 onward only.

Virtual SAN licensing / pricing

As far as I am aware there would be no issue with running a 6.5 Witness VM on a 6.0 cluster, provieded the Witness Appliance itself is managed by a 6.5 vCenter.

"In each node we will have 1 x 400GB cache and 2 x 600GB capacity tier disks."

Unless you plan to use very little percent of the storage I would advise larger (and multiple if possible) capacity drives, so that full repair in the event of a single disk on host is possible - your cache:capacity ratio would still be okay with far more than the current capacity per Disk-Group.

"How much usable capacity would this give us after the creation of 1 VSAN Data store with the disks from the 2 hosts?"

Assuming you are running it as FTT=1 mirrored on both date-nodes this will give you 1.2TB usable space (e.g. 1.2TB of vmdks) - however guidelines in general are to not utilize more than ~70-75% of vsandatastore as resyncs and reconfigurations of vSAN Objects temporarily needs space to do this (plus for other factors such as snapshots and/or backup temporarily storing data on vsandatastore). That utilisation recommendation is generally also advised for the purpose of recovery resync to rebuild failed components, but this isn't possible in the event of a node failure in a 2-node configuration (FTT=1 requires 3 usable Fault Domains), and for full recovery of a single disk failure you would require whatever % space the disk makes up of the Disk-Group(s) on that node.

"If we expand in the future is it just a simple case of adding disks into both hosts and expanding the data store?"

Yes, drives added to existing Disk-Groups add this storage to the vsandatastore automatically.

Do make sure you know how many slots these servers come with available and in what SFF so that you know you can expand by adding disks as opposed to having to replace existing disks with larger ones.

"Is that correct or is there a specific license key for the witness VM?"

Witnesses typically are run as a VM on one site/cluster and then are registered as a Witness Appliance in the same vCenter as the vSAN cluster - these 'hosts' come with their own special free licence.

"The witness states it needs a cache and capacity tier, we don’t have any SSD in the environment but I believe for the witness you don’t need SSD. Would this be correct?"

These don't require physical local disks as data-nodes do - only vmdks for the VM backing the Witness Appliance (stored wherever, do not need to be flash for cache etc.),

Here are the sizing guidelines for these

https://storagehub.vmware.com/t/vmware-vsan/vsan-stretched-cluster-2-node-guide/witness-host-sizing/

And the connection requirements from Witness to Data-nodes:

https://blogs.vmware.com/virtualblocks/2015/09/11/vmware-virtual-san-robo-edition/

Witness Network Connectivity Requirements

- 1.5 Mbps connectivity

- 500 milliseconds latency RTT

- Layer 3 network connectivity without multicast to the nodes in the cluster

"I assume we won’t have the issue with the VSAN for ROBO licensing which is limited to 25 VMs, would that be correct?"

Only ROBO per-VM licensed packs have VM quantity limitations AFAIK (I work in GSS - Licensing is handled by another group - if you have existing S&S I am sure you could get further clarification on this from them by opening a Support Request)

I hope this answers your questions.

Bob

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Enthusiast
Enthusiast

Many Thanks Bob for the clarity provided thats really helpful, thank you.

"Is that correct or is there a specific license key for the witness VM?"

Witnesses typically are run as a VM on one site/cluster and then are registered as a Witness Appliance in the same vCenter as the vSAN cluster - these 'hosts' come with their own special free licence.

yes the witness will be in the same vcenter but in a different cluster, so this should work. How would we acquire the free license key for this? Do you happen to know.

"I believe we need to do this to allow us the use of ROBO functionality which is a feature in 6.5."

ROBO existed in 6.0 (6.1), sounds like you are you setting this up as a 2-Node Direct Connect? - This is 6.5 onward only.

As far as I am aware there would be no issue with running a 6.5 Witness VM on a 6.0 cluster, provieded the Witness Appliance itself is managed by a 6.5 vCenter.

yes thats what we want to run, the 2 node direct connect. Our plan is to at least upgrade vcenter to 6.5 but use the appliance rather than a Windows server to achieve this, as it seems that is Vmware best practise model now.

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VMware Employee
VMware Employee

Hello ictadminrbassi

"How would we acquire the free license key for this? Do you happen to know."

It comes with it, it is an 'embedded licence' - you can test deploying a Witness Appliance at any time if you want to see this yourself:

https://my.vmware.com/web/vmware/details?productId=646&downloadGroup=WITNESS-OVA-65-D

Though don't try configuring this using the C# Client or it will use a trial license, not the embedded one - use the Web Client:

https://kb.vmware.com/s/article/2145456

"Our plan is to at least upgrade vcenter to 6.5 but use the appliance rather than a Windows server to achieve this, as it seems that is Vmware best practise model now."

Yes, either way I would advise upgrading to vCSA 6.5, lots of added features and optimisations compared to Windows-based 6.0.

Bob

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Expert
Expert

"As far as I am aware there would be no issue with running a 6.5 Witness VM on a 6.0 cluster, provieded the Witness Appliance itself is managed by a 6.5 vCenter."

I can verify that this works. At one of my customers, their Witness Appliances are hosted on a 6.0 environment. They are however registered in the same 6.5 vCenter as the ROBO's are. The 6.0 Platform is basically just somewhere for the Witness Appliances "to live". They need to run somewhere after all.

Please be mindful that Witness Appliances must be registered (added) directly on/under the "Datacenter" level and not on a "Cluster" level. Create a new Datacenter object in vCenter, call it something like "vSAN Witnesses" or something meaningful and add the Witness Appliance(s) directly under it (there are no "clusters" in this "Datacenter" Object).

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Enthusiast
Enthusiast

Thank you I wasnt aware of that. 

Please be mindful that Witness Appliances must be registered (added) directly on/under the "Datacenter" level and not on a "Cluster" level. Create a new Datacenter object in vCenter, call it something like "vSAN Witnesses" or something meaningful and add the Witness Appliance(s) directly under it (there are no "clusters" in this "Datacenter" Object).

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Immortal
Immortal

2 Node is an architecture.

ROBO is a license.


2 Node vSAN can use any license

vSAN ROBO licensing can use 2-64 nodes

VMware vSAN ROBO Licensing & vSAN 2 Node - Virtual Blocks

Jase McCarty - Field SA @PureStorage - @jasemccarty
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