Yellow Bricks

by Duncan Epping

virtual san

Site locality in a vSAN Stretched Cluster?

· · 7 Comments

On the community forums, a question was asked around the use of site locality in a vSAN Stretched Cluster. When you create a stretched cluster in vSAN you can define within a policy how the data needs to be protected. Do you want to replicate across datacenters? Do you want to protect the “site local data” with  RAID-1 or RAID-5/6? All of these options are available within the UI.

What if you decide to not stretch your object across locations, is it mandatory to specify which datacenter the object should reside in?

The answer is simple: no it is not. The real question, of course is, would be: should you define the location? Most definitely! If you wonder how to do this, simplicy specify it within the policy you define for these objects as follows:

The above screenshot is taken from the H5 client, if you are still using the Web Client it probably looks slightly different (Thanks Seamus for the screenshot):

Why would you do this? Well, that is easy to explain. When the objects of a VM get provisioned the decision will be made per object where to place it. If you have multiple disks, and you haven’t specified the location, you could find yourself in the situation where disks of a single non-stretched VM are located in different datacenters. This is, first of all, terrible for performance, but maybe more importantly also would impact availability when anything happens to the network between the datacenters. So when you use site locality for non-stretched VMs, make sure to also configure the location so that your VM and objects will align as demonstrated in the below diagram.

 

Device X is not listed on the vSAN Compatability Guide, can I still use it?

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I get this question almost daily, and I am pretty sure I have said this various times, but just in case it wasn’t clear I figured I would share the answer to the question whether a device should be used in a vSAN cluster when it is not listed on the vSAN Compatibility Guide? if you have not looked at the components variant of the VCG for vSAN please take a look here: http://vmwa.re/vsanhclc. Of course, we also have an easier route, which is the ReadyNode VCG. But some may want to tweak based on performance, cost etc. I get that, and so does VMware, that is why we have listed all supported and tested components. Can you use a device which is not listed? Sure you can. Will VMware support the environment? Maybe they will, maybe they won’t! Should you use a device which is not listed if the previous answer is maybe? No!

So let’s be clear and let’s answer the two most asked questions:

  • Device X is not listed on the vSAN Compatability Guide, can I still use it?
    • No, you should not. If any problem arises chances are you will not get the support you need as a result of an unsupported configuration. Sure, usually VMware Support will do their best to help, but if it appears the unsupported device is causing the problem then it becomes difficult. Please do not use devices which are not listed
  • Device X is listed with Firmware version Y, but the OEM says I should use Z, what to do?
    • Ask the OEM why the version is not listed on VMware’s VCG website. Vendors are responsible for certifying components and the software (drivers / firmware) associated with it. If it is not listed then it has either not been submitted yet, it has not been tested, or it has not passed the test. Please only use tested and listed versions, the only exception is when both VMware GSS and the OEM points you to a new version.

Hope that helps,

New book: VMware vSAN 6.7 U1 Deep Dive

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Cormac Hogan and I have been working late nights and weekends over the past months to update our vSAN book material. Thanks Cormac, it was once again a pleasure working with you on this project! As you may know, we released two versions of a vSAN based book through VMware Press. The book was titled vSAN Essentials. As mentioned before, after restructuring and rewriting a lot of the content we felt that the title of the book didn’t match the content, so we decided to rebrand it to vSAN 6.7 U1 Deep Dive. After receiving very thorough reviews by Frank Denneman and Pete Koehler (Thanks guys!) we managed to complete it this week after we added a great foreword by our business unit’s SVP and General Manager, Yanbing Li.

Cormac and I decided to take the self-publishing route for this book, which allows us to set a great price for the ebook and enable the Amazon matchbook option, giving everyone who buys the paper version through Amazon the option to buy the e-book with a nice discount! As prices will vary based on location I am only going to list the USD prices. Please check your local Amazon website for localized prices. Oh, and before I forget, I would like to recommend buying the ebook flavor! Why? Well:

“On average, each printed book releases 8.85 pounds of carbon dioxide into the environment. Together, the newspaper and book-printing industries cut down 125 million trees per year and emit 44 million tons of CO2.”

We appreciate all support, but we prefer the cleanest option from an environmental stance, this is also the reason we priced the ebook a lot cheaper than the paper version. Anyway, here are the links to the US store, we hope you enjoy the content, and of course as always an Amazon review would be appreciated! Interestingly, it seems we already reached number 1 in the category Virtualization and the category Storage before this announcement, thanks everyone, we really appreciate it! (Please note, as an Amazon Associate I earn from below qualifying purchases.)

 

UPDATE:

It appears that some Amazon stores take a bit longer to index the content, so listing all the different versions below for the different stores that sell it:

vSAN Adaptive Resync, what does it do?

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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,

Where is the vSAN storage performance proactive test in vSphere 6.5 U1 patch 02?

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I had some customers asking where the storage performance proactive test and the multicast proactive test was in the latest release of vSAN. In the past this is what the UI looked like when they would go to the Proactive Test section:

proactive test disappeared

But now it looks like this:

proactive test disappeared

What happened? Well, two tests have been removed. I guess most people will understand why the Multicast test has been removed, with the disappearance of Multicast in vSAN the test was not needed any longer. To be clear, if you are running vSAN in unicast mode the test will not show, if you are running in multicast mode however then of course the test will still be shown. But what about the Storage Performance Test?

We have noticed that most customers were using HCI Bench when doing benchmarks or using their own tooling (please don’t use legacy tools). Those who were using the proactive test often drew incorrect conclusions as it does not provide the flexibility a solution like HCI Bench offers. VMware felt that HCI Bench was a more suitable solution for doing benchmarks and this is definitely VMware’s recommended solution, as such the decision was made to focus on HCI Bench from a development perspective and deprecate the perf benchmark feature in the Proactive Tests section.