ironic/doc/source/install/include/disk-label.rst

Choosing the disk label

Note

The term disk label is historically used in Ironic and was taken from parted. Apparently everyone seems to have a different word for disk label - these are all the same thing: disk type, partition table, partition map and so on...

Ironic allows operators to choose which disk label they want their bare metal node to be deployed with when Ironic is responsible for partitioning the disk; therefore choosing the disk label does not apply when the image being deployed is a whole disk image.

There are some edge cases where someone may want to choose a specific disk label for the images being deployed, including but not limited to:

• For machines in bios boot mode with disks larger than 2 terabytes it's recommended to use a gpt disk label. That's because a capacity beyond 2 terabytes is not addressable by using the MBR partitioning type. But, although GPT claims to be backward compatible with legacy BIOS systems that's not always the case.
• Operators may want to force the partitioning to be always MBR (even if the machine is deployed with boot mode uefi) to avoid breakage of applications and tools running on those instances.

The disk label can be configured in two ways; when Ironic is used with the Compute service or in standalone mode. The following bullet points and sections will describe both methods:

• When no disk label is provided Ironic will configure it according to the boot mode (see boot_mode_support); bios boot mode will use msdos and uefi boot mode will use gpt.
• Only one disk label - either msdos or gpt - can be configured for the node.

When used with Compute service

When Ironic is used with the Compute service the disk label should be set to node's properties/capabilities field and also to the flavor which will request such capability, for example:

ironic node-update <node-uuid> add properties/capabilities='disk_label:gpt'

As for the flavor:

nova flavor-key baremetal set capabilities:disk_label="gpt"

When used in standalone mode

When used without the Compute service, the disk label should be set directly to the node's instance_info field, as below:

ironic node-update <node-uuid> add instance_info/capabilities='{"disk_label": "gpt"}'