Yellow Bricks

by Duncan Epping

vSphere

What if the disk controller driver included in my vendor’s ESXi image is not on the vSAN HCL?

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Sometimes unfortunately there are situations where a vendor’s ESXi image includes a disk controller driver that is not on the vSAN HCL/VCG (VMware Compatibility Guide). Typically it is a new version of the driver which is supported for vSphere, but not yet for vSAN. In that situation, what should you do? So far there are two approaches I have seen customers take:

  1. Keep running with the included driver and wait for the driver to be supported and listed on the vSAN HCL/VCG
  2. Downgrade the driver to the version which is listed on the vSAN HCL/VCG

Personally, I feel that option 2 is the correct way to go. The reason is simple, vSphere and vSAN have different certification requirements for disk controllers and the vSAN certification criteria are just more stringent than vSphere’s. Hence, sometimes you see vSAN skipping certain versions of drivers, this usually means a version did not pass the tests. Now, of course, you could keep running the driver and wait for it to appear on the vSAN HCL/VC. If however, you hit a problem, VMware Support will always ask you first to bring the environment to a fully supported state. Personally, I would not want the extra stress while troubleshooting. But that is my experience and preference. Just to be clear, from a VMware stance, there’s only one option, and that is option two, downgrade to the supported version!

Is a crossover cable needed for vSAN 2-Node Direct Connect?

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I had this question last week around vSAN 2-node direct connect and whether using a crossover cable is still required to be used or if a regular CAT6 cable (CAT 5E works as well) can be used. I knew the answer and figured this would be documented somewhere, but it doesn’t appear to be. To be honest, many websites when talking about the need for crossover cables are blatantly wrong. And yes, I also spotted some incorrect recommendations in VMware’s own documentation, so I requested those entries to be updated. Just to be clear, with vSAN 2-Node Direct Connect, or vMotion, or any other service for that matter, you can use a regular CAT6 cable, combined with 10GbE (or faster) NICs, this gives you great performance without the cost of a 10GbE (or faster) switch. I can’t recall having seen a NIC in the past 10 years that does not have Auto MDI/MDI-X implemented, even though it was an optional feature in the 1000Base-T standard. In other words, there’s no need to buy a crossover cable, or make one, just use a regular cable.

Can’t have more than 255 characters in VM notes using the vSphere (h5) Client?

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I had a question about a limit a customer was hitting with the VM notes using the vSphere (H5) Client. They noticed that whenever they got around ~260 or so characters, they could not add any characters beyond that unless they deleted some. After talking to an engineer within VMware I found out that this is indeed the limit for the vSphere Client today. Through the API, and of course also PowerCLI, you can go beyond the 255 if needed. Also with the Web Client you could do this. If you are hitting this issue, please be aware that it is a known issue and VMware is looking to resolve it hopefully soon.

VMs which are not stretched in a stretched cluster, which policy to use?

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I’ve seen this question popping up regularly. Which policy setting (“site disaster tolerance” and “failures to tolerate”) should I use when I do not want to stretch my VMs? Well, that is actually pretty straight forward, in my opinion, you really only have two options you should ever use:

  • None – Keep data on preferred (stretched cluster)
  • None – Keep data on non-preferred (stretched cluster)

Yes, there is another option. This option is called “None – Stretched Cluster” and then there’s also “None – Standard Cluster”. Why should you not use these? Well, let’s start with “None – Stretched Cluster”. In the case of “None – Stretched Cluster”, vSAN will per object decide where to place it. As you hopefully know, a VM consists of multiple objects. As you can imagine, this is not optimal from a performance point of view, as you could end up having a VMDK being placed in Site A and a VMDK being placed in Site B. Which means it would read and write from both locations from a storage point of view, while the VM would be sitting in a single location from a compute point of view. It is also not very optimal from an availability stance, as it would mean that when the intersite link is unavailable, some objects of the VM would also become inaccessible. Not a great situation. What would it look like? Well, potentially something like the below diagram!

Then there’s “None – Standard Cluster”, what happens in this case? When you use “None – Standard Cluster” with “RAID-1”, what is going to happen is that the VM is configured with FTT=1 and RAID-1, but in a stretched cluster “FTT” does not exist, and FTT automatically will become PFTT. This means that the VM is going to be mirrored across locations, and you will have SFTT=0, which means no resiliency locally. It is the same as “Dual Site Mirroring”+”No Data Redundancy”!

In summary, if you ask me, “none – standard cluster” and “none – stretched cluster” should not be used in a stretched cluster.

vCLS VMs not powering on, insufficient resources error

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This week I had someone internally me asking about a situation where vCLS VMs (learn more about vSphere Cluster Service here.) were not powering on and an error was thrown stating “insufficient resources”. I had seen this issue before at some point and I knew it had something to do with the VM version and EVC. The details of the error messages seem to support that. The UI showed the following on the “power on virtual machine” task:

Insufficient resources

And then when you would look at the details of the error you could see the following:

The target host does not support the virtual machine's current hardware requirements.

Or you could see:

Feature 'MWAIT' was absent, but must be present.

So how do you solve this problem? First of all, this could be two different problems. We solved it the following way, please note that the second option was just us fiddling around to get the VMs provisioned and powered-on, and this is not the official VMware procedure to get it working. I have reported this to the engineers to figure out why this happens, and to get it fixed. There are two options, please use Option 1, as this is a requirement for EVC and the recommended method when you see the “MWAIT” error:

Option 1:

Verify if “Monitor/MWAIT” is set to Enabled in the BIOS. If it is set to Disabled, then this is why the power-on fails. vCLS has per-VM EVC enabled on the VM.

If you can’t enable Monitor/MWAIT, then below is the procedure for disabling “per VM EVC” for the provisioned vCLS VMs.

Option 2:

  1. Upgrade the VM’s “Compatibility” version to at least “VM version 14” (right-click the VM)
  2. Click on the VM, click on the Configure tab and click on “VMware EVC”
  3. Click on “Edit” and click on “Yes” when you are informed to not make changes to the VM
  4. Disable “EVC”
  5. Repeat for the other vCLS VMs

I want to mention cosmin.gq, as it seems the issue (and resolution with regards to disabling EVC) was also reported on that blog, and considering they reported it in October already it only seems fair to mention them here also.