Yellow Bricks

by Duncan Epping

vsan

vSAN ESA Witness memory and CPU resources?

· · Leave a Comment

Not sure when this happened, but somehow the resource requirements for the vSAN Witness VM disappeared. Someone asked me last week how much memory is allocated to a VM, and how many vCPUs. Now, of course, this depends on the profile you select as the Witness VM has an M, L, and XL profile. The profile you select is determined by the number of VMs you will be provisioning, yes it is smart to take a growth factor into account. Now, when you deploy the VM, it doesn’t give a hint either, but you can figure out the size by simply looking at the OVF descriptor file. So this is what I got from the vSAN ESA Witness OVF:

  • vSAN ESA Witness XL – 8 vCPUs – 64 GB memory
  • vSAN ESA Witness L – 4 vCPUs – 32 GB memory
  • vSAN ESA Witness M – 4 vCPUs – 16 GB memory

And for those who were wondering, with vSAN OSA the requirements are:

  • vSAN OSA Witness XL – 6 vCPUs – 32 GB memory
  • vSAN OSA Witness L – 2 vCPUs – 32 GB memory
  • vSAN OSA Witness Normal – 2 vCPUs – 16 GB memory
  • vSAN OSA Witness Tiny – 2 vCPUs – 8 GB memory

I hope that helps, and also please do note… if you read this article a few years from now, things may have changed!

#113 – Procuring hardware for a vSAN based VCF infrastructure – featuring John Nicholson!

· · Leave a Comment

I’ve been on the Virtually Speaking podcast several times, so it was time to invite one of the hosts to the Unexplored Territory Podcast and discuss his favorite topic, hardware configurations, and the bill of materials! John Nicholson goes over all the ins and outs of procuring new hardware and talks about ordering components for existing hardware. We discuss NICs, Switches, Ready Node configurations, Emulated Ready Node configurations, NVMe devices, and much more.

Especially in todays world of ever increasing memory prices, and difficulty to procure hardware, the suggestions John makes around re-using existing hardware with vSAN ESA are very valid. Also, the use of Memory Tiering is definitely something every customer should consider. But before I share all the nuggets, just listen to the episode on Spotify (bit.ly/4r66flp), Apple (apple.co/4raF5Kj), the embedded player below, or watch it on Youtube.

During the discussion, various blogs and videos were mentioned, make sure to check those as well!

Can I replicate, or snapshot, my vSAN Stretched Cluster Witness appliance for fast recovery?

· · Leave a Comment

I’ve been seeing this question pop up more frequently, can I replicate or snapshot my vSAN Stretched Cluster Witness appliance for fast recovery? Usually, people ask this question as they cannot adhere to the 3-site requirement for a vSAN Stretched Cluster. So by setting up some kind of replication mechanism with low RPO, they try to mitigate this risk.

I guess the question stems from a lack of understanding of what the witness does. The witness provides a quorum mechanism, the quorum mechanism helps determine which site has access to the data in the case of a network failure (ISL) between the data locations.

Can I replicate, or snapshot, my vSAN Stretched Cluster Witness appliance for fast recovery?

So why can the Witness Appliance not be snapshotted or replicated then? Well, in order to provide this quorum mechanism, the Witness Appliance stores a witness component for each object. This is not per site, or per VM, but for every object… So if you have a VM with multiple VMDKs, you will have multiple witness objects per VM stored on the witness appliance. That witness object holds metadata and, through a log sequence number, understands which object holds the most recent data. This is where the issue arises. If you revert a Witness Appliance to an earlier point in time, the witness components also revert to an earlier point in time, and will have a different log sequence number than expected. This results in vSAN being unable to make the object available to the surviving site, or the site that is expected to hold quorum.

So in short, should you replicate or snapshot the Witness Appliance? No!

 

vSAN to vSAN Replication and Recovery Plan creation demo!

· · 1 Comment

As I was going through the various recordings I had of demos I created for Explore, I realized I hadn’t published the demos I created for vSAN to vSAN Replication, and on creating a Recovery Plan based on a vSAN Protection Group in VMware Live Recovery. So here it is. It is a pretty lengthy video as I go through all the various steps involved. So what you will see in this demo is the following:

  • vCenter Server Pairing between my 2 sites
  • Cluster pairing
  • Creation of a vSAN Protection Group, including vSAN to vSAN Replication
  • Creation of a Recovery Plan based on the previously created Protection Group
  • Test of the Recovery Plan

What happens after a Site Takeover when my failed sites come back online again?

· · Leave a Comment

I got a question after the previous demo: what would happen if, after a Site Takeover, the two failed sites came back online again? I completely ignored this part of the scenario so far, I am not even sure why. I knew what would happen, but I wanted to test it anyway to confirm that what engineering had described actually happened. For those who cannot be bothered to watch a demo, what happens when the two failed sites come back online again is pretty straightforward. The “old” components of the impacted VMs are discarded, vSAN will recreate the RAID configuration as specified within the associated vSAN Storage Policy, and then a full resync will occur so that the VM is compliant again with the policy. Let me repeat one part: a full resync will occur! So if you do a Site Takeover, I hope you do understand what the impact will be. A full resync will take time, of course, depending on the connection between the data locations.