Yellow Bricks

by Duncan Epping

Various

vSAN Adaptive Resync, what does it do?

· ·

I am starting to get some more questions about vSAN Adaptive Resync lately. This was introduced a while back, but is also available in the latest versions of vSAN through vSphere 6.5 Patch 02. As a result various folks have started to look at it and are starting to wonder what it is. Hopefully by now everyone understands what resync traffic is and when you see resync traffic. The easiest example of course is a host failure. If a host has failed and there’s sufficient disk space and there’s additional hosts available to make the impacted VMs compliant with their policy again then vSAN will resync the data.

Resync aims to finish the creation of these new components asap, simple reason for this is availability. The longer the resync takes, the longer you are at risk. I think that makes sense right? In some cases however it may occur that when VMs are very busy and resync is happening that VM observed latency goes through the roof. We already had a manual throttling mechanism for when this situation occurs, but of course preferably vSAN should throttle resync traffic properly for you. This is what vSAN Adaptive Resync does.

So how does that work? Well, when the high watermark is reached for VM latency then vSAN will cut the bandwidth of resync in half. Next vSAN will check if the VM latency is below the low watermark, if not then it will cut resync traffic in half again. It does this until the latency is below the low watermark. When the latency is below the low watermark then vSAN will increase the bandwidth of resync traffic granularly until the low watermark is reached and stay at that level. (Some official info can be found in this kb, and this virtual blocks blog.)

Hope that helps,

Happy 10th Birthday Yellow-Bricks.com

· ·

Just wanted to share with all of you the fact that this week marks the 10th anniversary of Yellow-Bricks.com. Crazy thinking back about how it all started, and what it turned in to. Thanks everyone for taking the time to read and comment on many of the articles over the years. Those wondering what’s next, what to expect in the upcoming year? Well definitely an update to the vSAN Essentials book released yesterday, but also an update to probably one of the best sold VMware related books:

Powerpoint for Mac switching resolution?

· ·

I’ve had this issue for a long time. Whenever I would open PowerPoint and present using a projector all my diagrams and screenshot would show up fuzzy. Even if I would set up the screen configuration to be optimized for the projector it still would not look great. The funny thing is that I always have my screen setup in “mirror” mode, and this week I noticed that when I switched between my regular screen to Presenter Mode on PowerPoint that the resolution would change.

Apparently when you use presenter mode with PowerPoint on a Mac it sets the screens in “extended mode” automatically. By default it then seems to optimize for the Mac screen automatically, which usually does not work well for the projector considering most are low resolution devices. I disabled the Presenter Mode option next, and when I turned off presenter mode in PowerPoint it worked fine. You can switch it off in Preferences under Slide Show:

I normally don’t blog about this kind of stuff, but as I hardly was able to find anything useful about it anywhere I figured I would share it with the world.

Insufficient configured resources to satisfy the desired vSphere HA failover level

· ·

I was going over some of the VMTN threads and I noticed an issue brought up with Admission Control a while ago. Completely forgot about it until it was brought up again internally. With vSphere 6.5 and vSphere HA there seems to be a problem with some Admission Control Policies. When you for instance have selected the Percentage Based Admission Control Policy and you have a low number of hosts, you could receive the following error

Insufficient configured resources to satisfy the desired vSphere HA failover level on the cluster …

I managed to reproduce this in my lab, and this is what it looks like in the UI:

It seems to happen when there’s a minor difference in resources between the host, but I am not 100% certain about it. I am trying to figure out internally if it is a known issue or not, and will come back to this when I know in which patch it will be solved and/or if it is indeed a known issue.

 

Using HA VM Component Protection in a mixed environment

· ·

I have some customers who are running both traditional storage and vSAN in the same environment. As most of you are aware, vSAN and VMCP do not go together at this point. So what does that mean for traditional storage, as in with traditional storage for certain storage failure scenarios you can benefit from VMCP.

Well the statement around vSAN and VMCP is actually a bit more delicate. vSAN does not propagate PDL or APD in a way which VMCP understands. So you can enable VMCP in your environment, without it having an impact on VMs running on top of vSAN. The VMs which are running on the traditional storage will be able to use the VMCP functionality, and if an APD or PDL is declared on the LUN they are running on vSphere HA will take action. For vSAN, well we don’t propagate the state of a disk that way and we have other mechanisms to provide availability / resiliency.

In summary: Yes, you can enable HA VMCP in a mixed storage environment (vSAN + Traditional Storage). It is fully supported.