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Enhanced Linked Mode (ELM) vs Hybrid Linked Mode (HLM)

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In the last few weeks, albeit due to VMworld, I have seen a large number of inquiries from customers regarding the existing vCenter Enhanced Linked Mode (ELM) as it compares to the newly announced Hybrid Linked Mode (HLM) feature. In some cases, certain assumptions were being made based on what was initially announced and I think that also led to some confusion on what the future holds for both of these capabilities. Hopefully with this article, I can help clarify the differences between ELM and HLM and their respective use cases. I will also quickly touch upon some of the future thinkings for both of these features as they were discussed at several VMworld Sessions both in the US and Europe.

Disclaimer: Hopefully folks are familiar with the standard VMworld Disclaimer slide that is shown before any session which states features are subject to change and must not be included in contracts, purchase orders or sales agreement of any kind. I am sure many of you have memorized it by now, but this is a good time to re-iterate that point, especially as we talk about futures 🙂

Current

Lets start off by reviewing what we have today and explaining the differences between ELM and HLM.

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Correlating vSAN perf metrics from vSphere Web Client to both PowerCLI & vSAN Mgmt API

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While going through the PowerCLI 6.5.1 release notes last week, in addition to the new Get-VsanView cmdlet which exposes the complete vSAN Management API through PowerCLI, I had learned that we had also released a new Get-VsanStat cmdlet. This new cmdlet allows customers to easily retrieve the various vSAN Performance Metrics provided by the vSAN Performance Service.


The really nice thing about vSAN Performance Service is that all vSAN stats are now available directly in the vSphere Web Client, where as before, this information was only available as part of the vSAN Observer which was a completely different interface. The other huge benefit to using the vSAN Performance Service is that it also stores the historical stats compared to the vSAN Observer which was primarily used for real time troubleshooting. As of vSAN 6.6, the vSAN Observer has been deprecated and will only be used by GSS in limited scenarios, everything you were able to do with the vSAN Observer is now possible with the vSAN Performance Service.

While trying out the new Get-VsanStat cmdlet, I had found it to be quite difficult to easily map the vSAN metrics I saw in the UI to the specific PowerCLI query required to extract that information. The documentation was also quite light and only included a single sample and although some of the metrics could easily be deduced, there were many others that I was just unsure of. I had also tried using the vSAN Management API directly, thinking that I might have more luck but it was also challenging to use for other reasons and I still ran into the same problem which was how do I easily map what I saw from the UI down to the API or even associating that back to PowerCLI.

After spending a few days with BOTH PowerCLI and the vSAN Management API and with a bit of frustration, I think I have finally figured out how to map what I saw from the UI back to the both CLI and API. This was not an easy task as and I had to cross-reference multiple datasources to build up this mapping and I thought I would put together a reference which outlines this mapping so that others would have to go through the same pain. IMHO, this should be a pretty straight forward task. In addition, I have also provided a PowerCLI sample for each of the metric types as well as the associated vSAN Management API mapping as those differ in name as well. This hopefully should make it easy for anyone to start using either of these interfaces for collecting vSAN metrics from an Automation standpoint. As part of this exercise, I also ran into a variety of bugs which I have already filed internally and all this information has been feedback to Engineering teams to hopefully improve both our CLI and API in future updates.

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What logs do I get when I enable syslog in VCSA 6.5?

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The native remote syslog functionality in the vCenter Server Appliance (VCSA) for vSphere 6.5 introduces several new changes from vSphere 6.0. With some of the questions that I have been receiving on this topic, I figure it would be useful to take a closer look at some of the different behaviors and configuration differences. Hopefully by the end of this article, you will have a better understanding of the syslog capabilities in VCSA 6.5

Remote Syslog Configuration

In VCSA 6.0, to configure the remote syslog configuration, you needed to use the vSphere Web Client. Although this may have felt like a convenience, it also added an unnecessary dependency on both vCenter Single-Sign On (SSO) and the vSphere Web Client UI. In VCSA 6.5, the remote syslog configurations is now part of the VAMI UI (https://[VCSA]:5480) which is an out-of-band interface that can still function if either SSO or vCenter Server is down. Once you have saved your changes, the syslog client will automatically be restarted for the changes to go into effect. If you wish to disable the remote syslog functionality, simply click on the reset button.


Note: If you decide to use port 1514, I have found that you must use the TLS protocol rather than TCP or else it will not work.

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