When designing a vSAN host, one of the consideration to increase availability is by having multiple disk groups and multiple IO controllers within a host. The obvious benefit to this would be to reduce the impact in when a disk or IO controller fails.
When a decision is made to use multiple IO controllers to drive disk groups within a vSAN host, it is important that the failure domain of such configuration is aligned with the physical setup.
The following example depicts a scenario where the physical IO controller to disk cabling is not aligned to the logical creation of the disk group. In this case, if IO Controller A fails, the impact would be to both vSAN disk groups 1 and 2 negating one of the benefits of having dedicated controllers per disk group.
Misaligned physical cabling and logical disk group configuration
The second example here depicts a properly aligned physical IO controller to disk group disk cabling setup. In this case, should IO Controller A fail, the impact would be contained to disk group 1 only. The same for IO controller B where the impact is contained to disk group 2.
Properly aligned physical cabling and logical disk group configuration
How can I validate this?
How can one validate if the physical cabling is properly aligned to the logical disk group configuration I hear you ask?
Well, first is of course to physically inspect and ensure that the SAS / SATA cables from IO controller A is physically connected to the bays of the disks for disk group 1, IO controller B connected to disk group 2 and so on.
Secondly, you can validate that all the disks in each disk group is connected to the same vmhba adapter. Each IO controller would have a unique vmhba id assigned such as vmhba0, vmhba1, vmhba2 etc.