1. Proposed title of this feature request

[RFE] IPI baremetal installer - make estimated guess about best disk to install to

2. What is the nature and description of the request?

A customer could easily deploy servers with our tech preview assisted installer: https://www.openshift.com/blog/using-the-openshift-assisted-installer-service-to-deploy-an-openshift-cluster-on-metal-and-vsphere ; https://docs.openshift.com/container-platform/4.7/release_notes/ocp-4-7-release-notes.html

Not all nodes had the same disk configuration, and some would put slow disks first which showed up as /dev/sda. The assisted installer somehow seems to have detected the fastest disks and seems to have used these, according to our customer's comments.

On the other hand, for the IPI baremetal installer, we must configure device hints and the installer does not make a qualified guess about the best drive to install to.

>> "From previous experiments and introspection of an assisted installer successful deployment, we came to the conclusion that [the OpenShift IPI installer] is not tuned to use physical disks as root device."

>> "(...) I moved all the physical disks on all servers to the smart array manager, so that now all disks appear as logical volumes to Core OS. With this setting, I have been able to deploy with IPI on both /dev/sdb and /dev/sdh volumes on five nodes."
>> "=> Pending question on this issue: how to configure the IPI deployment to let the OpenShift installer guess the root device, in the same way the assisted installer does?"

The IPI installer uses OpenStack's ironic baremetal installer behind the scenes: https://docs.openstack.org/ironic/latest/

OpenStack's ironic baremetal installer does not have any way to make an estimated guess which disk might be the ideal one to use; instead, it relies on administrator configured root device hints: https://docs.openstack.org/project-deploy-guide/tripleo-docs/latest/provisioning/root_device.html

This is what's inherited by OpenShift's BMI feature: https://docs.openshift.com/container-platform/4.6/installing/installing_bare_metal_ipi/ipi-install-installation-workflow.html#root-device-hints_ipi-install-configuration-files

It would be nice to have a feature where OpenStack ironic / the IPI installer makes a "guess" about what is the best disk to install to, e.g. based on characteristics such as make/model/size as well as performance metrics.

3. Why does the customer need this? (List the business requirements here)
4. List any affected packages or components.