VMware VS4-ENT-PL-A - vSphere Enterprise Plus Setup Manual page 203

The following are remediation and reboot best practices for different situations:
If the compliance check shows devices whose aliases (for example, names such as vmhba3) are different
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from the reference host, then remediation is possible. The remediation will cause the device to names to
align exactly with the reference host.
The remediation step (for hosts not provisioned with Auto Deploy) always requires reboot.
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The remediation step for hosts provisioned with Auto Deploy is unnecessary. Reboot the host without
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remediation.
The compliance check step ignores extra devices on the host that were not on the reference host. You
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should choose the host with the fewest devices as the reference host.
Auto Deploy Device Alias Naming
In order to create uniform, persistent, and stable device naming across all hosts, the device alias profile
should be used with homogeneous hosts only. These are hosts that are all identically configured with the
same network and storage cards in the PCI bus. The device alias profile is mandatory for all hosts
provisioned with Auto Deploy.
In previous versions of vSphere, devices were named based on the order in which they enumerated in the
BIOS. VMware did not guarantee that devices in the same slot on the same bus would have the same name
when the system rebooted if any PCI bus configuration changes occurred in the interim. Some PCI bus
configuration changes might be adding or removing cards, or changes resulting from card malfunction. In
vSphere 5.5, a mapping now exists between the physical location of the device (bus address) of devices and
their names (aliases). This means that when ESXi hosts reboot, devices that have not physically moved are
guaranteed to have the same name.
N For systems with older versions of the BIOS, the older BIOS might not provide accurate location
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information for on-board devices. ESXi applies heuristics for this case to keep the alias stable, even for these
devices. Always bring the BIOS up to the latest level.
The heuristic is designed to keep built-in devices that lack proper BIOS information stable even when cards
in slots are added or removed. VMware cannot guarantee this will function under all conditions (for
example, if changes are made in the BIOS setting or if devices fail).
For normally installed hosts, the alias mapping is stored on the system's hard disk or USB boot device. For
hosts provisioned with Auto Deploy, the mapping is stored in the Host Profile (device alias sub-profile).
Because the mapping is critical to keep the device naming stable the device alias sub-profile should never be
disabled for hosts provisioned with Auto Deploy.
For installed hosts, the device alias sub-profile can be used to align the device names (aliases) between
multiple hosts. However, those hosts must be homogeneous for this to work. If the hosts are not
homogeneous, you should disable the device alias sub-profile.
To avoid errors, VMware advises that you do not edit the device alias configuration policy in the Host
Profile.
Upgrading Systems for Device Alias Profiles
In previous versions of ESXi, the device alias profile did not exist. Consider the following issues when you
upgrade from previous versions of ESXi to ESXi 5.5:
For installed hosts (host not provisioned with Auto Deploy), upgrading the ESXi host preserves aliases.
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After they are upgraded, aliases remain stable as long as the BIOS provides the information.
When upgrading the ESXi host provisioned with Auto Deploy image for a stateless cluster, the aliases
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will not change because ESXi 5.5 uses the same algorithm to generate aliases (even though the ESXi 5.x
host profile does not contain aliases). A new Host Profile should then be generated from the reference
host. This Host Profile does contain aliases.
VMware, Inc.
Chapter 7 Installing ESXi
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