# Setting the Root Device for Deployment¶

If your hardware has several hard drives, it’s highly recommended that you specify the exact device to be used during introspection and deployment as a root device. This is done by setting a root_device property on the node in Ironic. Please refer to the Ironic root device hints documentation for more details.

For example:

openstack baremetal node set <UUID> --property root_device='{"wwn": "0x4000cca77fc4dba1"}'


To remove a hint and fallback to the default behavior:

openstack baremetal node unset <UUID> --property root_device


Note that the root device hints should be assigned before both introspection and deployment. After changing the root device hints you should either re-run introspection or manually fix the local_gb property for a node:

openstack baremetal node set <UUID> --property local_gb=<NEW VALUE>


Where the new value is calculated as a real disk size in GiB minus 1 GiB to account for partitioning (the introspection process does this calculation automatically).

## Setting root device hints automatically¶

Starting with the Newton release it is possible to autogenerate root device hints for all nodes instead of setting them one by one. Pass the --root-device argument to the openstack overcloud node configure after a successful introspection. This argument can accept a device list in the order of preference, for example:

openstack overcloud node configure --all-manageable --root-device=sdb,sdc,vda


It can also accept one of two strategies: smallest will pick the smallest device, largest will pick the largest one. By default only disk devices larger than 4 GiB are considered at all, set the --root-device-minimum-size argument to change.

Note

Subsequent runs of this command on the same set of nodes does nothing, as root device hints are already recorded on nodes and are not overwritten. If you want to change existing root device hints, first remove them manually as described above.

Note

This command relies on introspection data, so if you change disk devices on the machines, introspection must be rerun before rerunning this command.

## Using introspection data to find the root device¶

If you don’t know the information required to make a choice, you can use introspection to figure it out. First start with Introspect Nodes as usual without setting any root device hints. Then use the stored introspection data to list all disk devices:

openstack baremetal introspection data save fdf975ae-6bd7-493f-a0b9-a0a4667b8ef3 | jq '.inventory.disks'


For python-ironic-inspector-client versions older than 1.4.0 you can use the curl command instead, see Accessing Introspection Data for details.

This command will yield output similar to the following (some fields are empty for a virtual node):

[
{
"size": 11811160064,
"rotational": true,
"vendor": "0x1af4",
"name": "/dev/vda",
"wwn_vendor_extension": null,
"wwn_with_extension": null,
"model": "",
"wwn": null,
"serial": null
},
{
"size": 11811160064,
"rotational": true,
"vendor": "0x1af4",
"name": "/dev/vdb",
"wwn_vendor_extension": null,
"wwn_with_extension": null,
"model": "",
"wwn": null,
"serial": null
}
]


You can use all these fields, except for rotational, for the root device hints. Note that size should be converted to GiB and that name, wwn_with_extension and wwn_vendor_extension can only be used starting with the Mitaka release. Also note that the name field, while convenient, may be unreliable and change between boots.

Do not forget to re-run the introspection after setting the root device hints.