Change default RootDiskController from ide to scsi for VMWare guests

[daviftorres]

problem

Environment

• CloudStack: 4.20.2
• VMware: 7.0.3

Issue

When a VMware zone is deployed, the default CloudStack template does not define the disk controller.

As a result, new instances get rootDiskController=ide and dataDiskController=osdefault.

However, inside the guest OS, the disk actually appears as SCSI, since VMware defaults to SCSI.

Problem

If you try to "Override root disk size" or "Override root disk offering" during instance creation, it fails.

This happens because CloudStack “guesses” the controller type as IDE, as it’s not defined in the template.

After creation, resizing of a volume also fails with the same error.

Solution

Add a custom setting to define the controller explicitly rootDiskController=scsi.

After this, new instances will be created successfully, with the correct controller automatically applied.

If the instances were already created, you don’t need to recreate them, changing the controller setting to scsi will resolve the issue.

Notes

Inside the guest, disks still appear as SCSI, confirming that VMware uses SCSI by default.

Additionally

The default template (which uses LVM and ext3) does not automatically expand to match the resized volume.

To simplify administration I would recommend a new template to be the default pulled one:

• Debian (like the System VMs) instead of CentOS.
• Avoid LVM because it adds complexity for basic tasks (like expanding the root filesystem).
• Swap files can replace swap partitions with similar performance.
  • Swap partitions at the end of the disk make resizing filesystem a real pain.

For generic templates, consider omitting swap entirely and users can add it later if needed.

versions

The versions of ACS, hypervisors, storage, network etc..

The steps to reproduce the bug

...

What to do about it?

As far as I know this template was created 15 years ago ;-)

[DaanHoogland]

@daviftorres , would #11750 be of help?

[daviftorres]

Hey @DaanHoogland , I can't say because the issue that I am reporting affects VMWare and the other PR appears to cover the KVM but I can't say if it would also skip for VMWare. In fact, with my very basic understanding I would do the opposite in VMWare, I would always enforce the SCSI as the controller because I think that is the recommended but I can test if any of the others also work (ide certainly doesn't)

[daviftorres]

So, I tested all the options this time.

buslogic fails to start.

lsisas1068 and pvscsi started but CentOS7 had a kernel panic that I guess it is a driver problem.

In summary, maybe the problem is that it is not preferring the osdefault option (SCSI) and it is preferring ide instead.

[daviftorres]

It seems there is a contradiction in the recommended/default disk controller for VMware.

The global setting shows ide as the default, and ide is listed as a valid option.

However, when an instance is created without specifying a controller, the guest OS actually sees a SCSI controller, even though the instance details still show ide.

On the other hand, when resizing a volume, the workflow appears to prefer ide, and that always fails claiming ide is not supported.

Looking at the code, it first checks for scsi, then for ide, and falls back to osdefault otherwise. That makes it look like scsi or osdefault is the effective default. In another part of the code, it even explicitly returns scsi as the default.

So at this point I am unsure what the intended or recommended default actually is, but it seems clear that using ide does not work in my tests.

[nvazquez]

Hi @daviftorres - sorry if unclear but just for clarification, are you proposing to change the default value of the setting vmware.root.disk.controller from ide to scsi? From my understanding, CloudStack is honouring the value of the setting for the template's root disk controller, does it also work properly changing the setting value to scsi instead of defining the template setting for rootDiskController?

[daviftorres]

@nvazquez, you’re right. From my review, the “default” setting isn’t consistent everywhere. While ide may work in some cases, I recommend using scsi because it supports disk resizing and is also the preferred option for VMware.

My bad that I posted so much that apparently lost focus.

[daviftorres]

@nvazquez, regarding your question about whether ACS honors the value of the template’s root disk controller setting, it appears that it does.

I updated the global setting and restarted the management server.

After that, I deployed a new instance using the standard template. The instance correctly came up with the root disk controller set to scsi, and I was also able to resize the disk without any issues.