Witness question

[vSohill]

Hi ,

Witness question again  ,

For Virtual SAN stretched Cluster an Appliance witness is an option. Does the witness function if I emulated the SSD with any any problems  ? Is there any special requirement than the minimum latency need to be taken if I placed in the Cloud (vCloud Air or Amazon are options in my case )?

[zdickinson]

Good afternoon, did you use all HDD and manually fake some of them to look like SSD?  I guess it would work, not sure about performance.

Here are the latency requirements per Duncan.  Thank you, Zach.

5ms RTT latency max between data sites

200ms RTT latency max between data and witness site

Both L3 and L2 are supported between the data sites

10Gbps bandwidth is recommended, dependent on the number of VMs this could be lower or higher, more guidance will be provided soon around this!

L3 is expected between data and the witness sites

100Mbps bandwidth is recommended, dependent on the number of VMs this could be lower or higher, more guidance will be provided soon around this!

Designing a Virtual SAN stretched cluster

[Jasemccarty · Accepted solution]

Hi vSohill‌,

I maintain the Virtual SAN Stretched Cluster & 2 Node Guide.

1) The witness does not require actual SSD devices. The witness ships with 3 (or more) drives. ESXi is installed on one, one is used for the caching requirement, and one (or more) is used for the capacity requirement. These capacity drives (vmdks) are different sizes are really particular to the number of objects you are protecting.

2) The witness bandwidth is dependent on the number of Objects you are protecting, and ensuring that all of them can be failed over within 5 seconds. The rule of thumb is 2Mbps for every 1000 objects on a Stretched Cluster / 2 Node Configuration. The minimum latency is 500ms RTT for 2 Node configs and 200ms RTT for configurations larger than 2 Nodes.

I put together a quick guidance paper around the bandwidth requirements here:
https://www.vmware.com/files/pdf/products/vsan/vmware-virtual-san-6.1-stretched-cluster-bandwidth-si...

The Stretched Cluster and 2 Node Guides are here:

Virtual SAN 6.1: https://www.vmware.com/files/pdf/products/vsan/VMware-Virtual-SAN-6.1-Stretched-Cluster-Guide.pdf

Virtual SAN 6.2: https://www.vmware.com/files/pdf/products/vsan/VMware-Virtual-SAN-6.2-Stretched-Cluster-Guide.pdf

These docs include content for both Stretched Clusters and 2 Node configurations. The original one for 6.1 did not include 2 Node configs, but was updated in January 16'.

[vSohill]

Thanks JasemccartyJasemccarty,

Great guidance.