Vmotion of a CBT-enabled VM having multi-writer disk(supported)

[PMPM789]

Hello 

We have VM's with shared disks and CBT is enabled. from vCenter 7, we are unable to migrate(live migrate) the VM(storage/host) when the CBT is enabled. Is there options to do CBT disabled without down time or options to do live migration or possible options for share disks storage migration without a downtime(if possible)

[farmersam1]

Did you find a solution?  We have upgraded to vCenter 7 and are having the same issue.

[KumaranG]

Is there any found for this query? We are facing same issue after upgrade VMware vCenter 7.0.

Is multiwrter option disbaled in the version 7.0?

[farmersam1]

You'll have to improvise, depending on your environment.  In our case, we had 2 SQL servers that were sharing a disk for future SQL clustering and log writing.  The SQL clustering was never implemented, so all we had to do was A) change the disk on SQL server #1 from Multi Writer to Not Shared, and B) use the windows OS to share the drive in SQL server #1, then map to that drive in SQL Server #2. 
Here is the chart KB that lists the features available with Multi Writer in vCenter 7: https://kb.vmware.com/s/article/1034165

There is a workaround for SQL, and that it to change the disks from SAN to vSAN.  May be more hassle than it is worth: https://kb.vmware.com/s/article/74786

[KumaranG]

Hi Fermersam,

Thanks for sharing the details. We are using Oracle database using for SAP application. Is there any alternate to enable both vMotion and incremental backups operations?

[AleksandarO]

We're facing similar issues at the company I work for. We're running several Oracle RAC clusters on VMware and up until vCenter 6.7 having CTK enabled for the (non-shared) OS- and Oracle-binary-disks wasn't an issue as long as CTK was disabled for the shared Multi-Writer Oracle ASM disks.

After upgrading to vCenter 7 we started to experience all sorts of issues:

-the RAC VMs (having both Multi-Writer disks and CTK enabled) suddenly couldn't be powered on again once they were turned off

-adding new Multi-Writer disk to those VMs was also no longer possible

(because this has been a few moths ago I can't remember whether vMotion had been affected as well)

Fortunately we found out that it is possible to disable CTK without requiring a downtime using the PowerCLI APIs.

Our RAC VMs have been running fine with vCenter 7 since we disabled CTK.

But of course disabling CTK came with the downside that the backup jobs backing up those RAC VMs do now not only run significantly longer but do also consume way more resources than they did when CTK was still enabled.

It's kinda hard for me to believe that sthg which had been perfectly working before in vCenter 6.7 is now suddenly deemed "unsupported" in vCenter 7 for no (obvious) reason?

Since I have limited privileges in the vSphere environment at work, I just did some testing in my personal vSphere environment at hoeme (a single ESXi-7.0U3l host + vCenter 7.0.3 Build 21477706 licensed using the "vSphere Essentials Kit"):

My initial Setup: 2 Linux Test VMs with CTK enabled and no Multi-Writer disks

-adding Multi-Writer disks through PowerCLI connected to vCenter fails with "The operation is not supported on the object. CBT-enabled VM having multi-writer disk(s) is not supported"

-Disabling CTK online using PowerCLI connected to vCenter works

-after disabling CTK online, adding Multi-Writer Disks through PowerCLI connected to vCenter works

-trying to re-enable CTK online using PowerCLI connected to vCenter fails with "The operation is not supported on the object. CBT-enabled VM having multi-writer disk(s) is not supported"

-trying to re-enable CTK online using PowerCLI connected directly to the ESXi host works

-powering on a VM with CTK enabled and also having Multi-Writer disks works even through vCenter (although I'm pretty sure that this didn't work a few months ago when we first ran into vSphere 7 CTK/Multi-Writer disk related issues at work)

The fact that re-enabling CTK for a VM with Multi-Writer disks (even doings so online!) works flawlessly when connecting PowerCLI directly to the ESXi 7 host ("bypassing" vCenter) and that it did also work flawlessly before with vCenter 6.7 does quiet honestly make me wonder whether this is a bug in vCenter 7?

When you enable CTK for a VM which has Multi-Writer disks using PowerCLI, it does even correctly exclude the actual Multi-Writer disks from CTK while enabling it for the VM itself and all its non-shared disks.

I'll try apply the latest patches to my home vCenter server this weekend and see if that makes any difference ...

I'll keep you posted on how it goes 🙂

Best wishes,

Aleksandar

[mannharry]

hello ,

Please details should clarify:

CBT (CTK) feature is not supported on VMs with Multi-Writer Flag enabled. See - https://kb.vmware.com/s/article/1034165 (VMFS) & https://kb.vmware.com/s/article/2121181 (vSAN) for more details

In vSphere 7.x, the Multi-writer flag MUST not be enabled on Microsoft Windows Server Failover Cluster (WSFC) VMs. See KB - https://kb.vmware.com/s/article/79616 for more details.

vMotion is supported for Oracle RAC VMs only when Multi-writer flag is enabled. So, in this case, Multi-writer flag is not supposed to be disabled. KB 1034165

Regards

Harry

[AleksandarO]

Hello thanks for providing all these information.

I know that KB article which says that CTK is is not supported at all for VMs having Multi-Writer disks, but the same KB article does also state that it is supposedly unsupported to migrate ANY (including non-shared) disks of a VM having Multi-Writer disks using Storage vMotion. And I know that doing so DOES most definitely work even in vCenter 7 (we tried it with a non-critical test VM at work).

Also I don't see why VMware would suddenly decide to de-support a feature which has been working perfectly fine in earlier versions for no obvious reason? Why would they deliberate reduce the features of their product without offering an alternative and without giving any technical reason for doing so?

As I mentioned before, all this makes me wonder whether this might be just a bug in vCenter 7 along with a KB article which might have been updated in order to reflect that bug?

As for patching my home vCenter, I just checked and (besides from vCenter 8, which is not supported on my current CPU generation) it turns out that my patch level is already the latest.

Best wishes,

Aleksandar

[RajeevVCP4]

No ! there is no other option 

https://kb.vmware.com/s/article/2110452

[mannharry]

• It was even not supported not in 6.7 but its wasn't hard limitation  
• But with VC 7. x its a hard limitation that compute vmotion is not gonna work for VM having CBT and multi-writer disk.
• You will not be able to power on the VM with both those applied on VC 7. x.
• If you still have queries on this would suggest raising an SR with GS.

Regards

Harry