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Taikun OCP Guide

Table of Contents

RAID Configuration


Ironic supports RAID configuration for bare metal nodes. It allows
operators to specify the desired RAID configuration via the
OpenStackClient CLI or REST API. The desired RAID configuration is
applied on the bare metal during manual cleaning.

The examples described here use the OpenStackClient CLI; please see
for their corresponding REST API requests.


The bare metal node needs to use a hardware type that supports RAID
configuration. RAID interfaces may implement RAID configuration either
in-band or out-of-band. Software RAID is supported on all hardware,
although with some caveats – see Software
for details.

In-band RAID configuration (including software RAID) is done using
the Ironic Python Agent ramdisk. For in-band hardware RAID
configuration, a hardware manager which supports RAID should be bundled
with the ramdisk.

Whether a node supports RAID configuration could be found using the
CLI command baremetal node validate <node>. In-band
RAID is usually implemented by the agent RAID

agent ramdisk which supports RAID configuration

For doing in-band hardware RAID configuration, Ironic needs an agent
ramdisk bundled with a hardware manager which supports RAID
configuration for your hardware. For example, the DIB_raid_support should be
used for HPE Proliant Servers.


For in-band software RAID, the agent ramdisk does not need to be
bundled with a hardware manager as the generic hardware manager in the
Ironic Python Agent already provides (basic) support for software

RAID configuration JSON

The desired RAID configuration and current RAID configuration are
represented in JSON format.

Target RAID configuration

This is the desired RAID configuration on the bare metal node. Using
the OpenStackClient CLI (or REST API), the operator sets
target_raid_config field of the node. The target RAID
configuration will be applied during manual cleaning.

Target RAID configuration is a dictionary having
logical_disks as the key. The value for the
logical_disks is a list of JSON dictionaries. It looks

  "logical_disks": [
    {<desired properties of logical disk 1>},
    {<desired properties of logical disk 2>},

If the target_raid_config is an empty dictionary, it
unsets the value of target_raid_config if the value was set
with previous RAID configuration done on the node.

Each dictionary of logical disk contains the desired properties of
logical disk supported by the hardware type. These properties are
discoverable by:

baremetal driver raid property list <driver name>

Mandatory properties

These properties must be specified for each logical disk and have no
default values:

  • size_gb – Size (Integer) of the logical disk to be
    created in GiB. MAX may be specified if the logical disk
    should use all of the remaining space available. This can be used only
    when backing physical disks are specified (see below).
  • raid_level – RAID level for the logical disk. Ironic
    supports the following RAID levels: 0, 1, 2, 5, 6, 1+0, 5+0, 6+0.

Optional properties

These properties have default values and they may be overridden in
the specification of any logical disk. None of these options are
supported for software RAID.

  • volume_name – Name of the volume. Should be unique
    within the Node. If not specified, volume name will be
  • is_root_volume – Set to true if this is
    the root volume. At most one logical disk can have this set to
    true; the other logical disks must have this set to
    false. The root device hint will be saved, if
    the RAID interface is capable of retrieving it. This is
    false by default.

Backing physical disk hints

These hints are specified for each logical disk to let Ironic find
the desired disks for RAID configuration. This is machine-independent
information. This serves the use-case where the operator doesn’t want to
provide individual details for each bare metal node. None of these
options are supported for software RAID.

  • share_physical_disks – Set to true if this
    logical disk can share physical disks with other logical disks. The
    default value is false, except for software RAID which
    always shares disks.
  • disk_typehdd or ssd. If
    this is not specified, disk type will not be a criterion to find backing
    physical disks.
  • interface_typesata or scsi
    or sas. If this is not specified, interface type will not
    be a criterion to find backing physical disks.
  • number_of_physical_disks – Integer, number of disks to
    use for the logical disk. Defaults to minimum number of disks required
    for the particular RAID level, except for software RAID which always
    spans all disks.

Backing physical disks

These are the actual machine-dependent information. This is suitable
for environments where the operator wants to automate the selection of
physical disks with a 3rd-party tool based on a wider range of
attributes (eg. S.M.A.R.T. status, physical location). The values for
these properties are hardware dependent.

  • controller – The name of the controller as read by
    the RAID interface. In order to trigger the setup of a Software RAID via
    the Ironic Python Agent, the value of this property needs to be set to

  • physical_disks – A list of physical disks to use as
    read by the RAID interface.

    For software RAID physical_disks is a list of device
    hints in the same format as used for root-device-hints. The number of provided hints must
    match the expected number of backing devices (repeat the same hint if


If properties from both “Backing physical disk hints” or “Backing
physical disks” are specified, they should be consistent with each
other. If they are not consistent, then the RAID configuration will fail
(because the appropriate backing physical disks could not be found).

Examples for

Example 1. Single RAID disk of RAID level 5 with all of the
space available. Make this the root volume to which Ironic deploys the

  "logical_disks": [
      "size_gb": "MAX",
      "raid_level": "5",
      "is_root_volume": true

Example 2. Two RAID disks. One with RAID level 5 of 100 GiB
and make it root volume and use SSD. Another with RAID level 1 of 500
GiB and use HDD:

  "logical_disks": [
      "size_gb": 100,
      "raid_level": "5",
      "is_root_volume": true,
      "disk_type": "ssd"
      "size_gb": 500,
      "raid_level": "1",
      "disk_type": "hdd"

Example 3. Single RAID disk. I know which disks and
controller to use:

  "logical_disks": [
      "size_gb": 100,
      "raid_level": "5",
      "controller": "Smart Array P822 in Slot 3",
      "physical_disks": ["6I:1:5", "6I:1:6", "6I:1:7"],
      "is_root_volume": true

Example 4. Using backing physical disks:

  "logical_disks": [
      "size_gb": 50,
      "raid_level": "1+0",
      "controller": "RAID.Integrated.1-1",
      "volume_name": "root_volume",
      "is_root_volume": true,
      "physical_disks": [
      "size_gb": 100,
      "raid_level": "5",
      "controller": "RAID.Integrated.1-1",
      "volume_name": "data_volume",
      "physical_disks": [

Example 5. Software RAID with two RAID devices:

  "logical_disks": [
      "size_gb": 100,
      "raid_level": "1",
      "controller": "software"
      "size_gb": "MAX",
      "raid_level": "0",
      "controller": "software"

Example 6. Software RAID, limiting backing block devices to
exactly two devices with the size exceeding 100 GiB:

  "logical_disks": [
      "size_gb": "MAX",
      "raid_level": "0",
      "controller": "software",
      "physical_disks": [
        {"size": "> 100"},
        {"size": "> 100"}

Current RAID configuration

After target RAID configuration is applied on the bare metal node,
Ironic populates the current RAID configuration. This is populated in
the raid_config field in the Ironic node. This contains the
details about every logical disk after they were created on the bare
metal node. It contains details like RAID controller used, the backing
physical disks used, WWN of each logical disk, etc. It also contains
information about each physical disk found on the bare metal node.

To get the current RAID configuration:

baremetal node show <node-uuid-or-name>


  • Operator configures the bare metal node with a hardware type that
    has a RAIDInterface other than no-raid. For
    instance, for Software RAID, this would be agent.

  • For in-band RAID configuration, operator builds an agent ramdisk
    which supports RAID configuration by bundling the hardware manager with
    the ramdisk. See Build
    agent ramdisk which supports RAID configuration
    for more

  • Operator prepares the desired target RAID configuration as
    mentioned in Target RAID
    . The target RAID configuration is set on the Ironic

    baremetal node set <node-uuid-or-name> \
       --target-raid-config <JSON file containing target RAID configuration>

    The CLI command can accept the input from standard input also:

    baremetal node set <node-uuid-or-name> \
       --target-raid-config -
  • Create a JSON file with the RAID clean steps for manual cleaning.
    Add other clean steps as desired:

      "interface": "raid",
      "step": "delete_configuration"
      "interface": "raid",
      "step": "create_configuration"


    ‘create_configuration’ doesn’t remove existing disks. It is
    recommended to add ‘delete_configuration’ before ‘create_configuration’
    to make sure that only the desired logical disks exist in the system
    after manual cleaning.

  • Bring the node to manageable state and do a
    clean action to start cleaning on the node:

    baremetal node clean <node-uuid-or-name> \
       --clean-steps <JSON file containing clean steps created above>
  • After manual cleaning is complete, the current RAID configuration
    is reported in the raid_config field when running:

    baremetal node show <node-uuid-or-name>

Software RAID

Building Linux software RAID in-band (via the Ironic Python Agent
ramdisk) is supported starting with the Train release. It is requested
by using the agent RAID interface and RAID configuration
with all controllers set to software. You can find a
software RAID configuration example in raid-config-examples.

There are certain limitations to be aware of:

  • Only the mandatory properties (plus the required
    controller property) from Target RAID configuration are
    currently supported.

  • The number of created Software RAID devices must be 1 or 2. If
    there is only one Software RAID device, it has to be a RAID-1. If there
    are two, the first one has to be a RAID-1, while the RAID level for the
    second one can be 0, 1, 1+0, 5, or 6. As the first RAID device will be
    the deployment device, enforcing a RAID-1 reduces the risk of ending up
    with a non-booting node in case of a disk failure.

  • Building RAID will fail if the target disks are already
    partitioned. Wipe the disks using e.g. the
    erase_devices_metadata clean step before building RAID:

      "interface": "raid",
      "step": "delete_configuration"
      "interface": "deploy",
      "step": "erase_devices_metadata"
      "interface": "raid",
      "step": "create_configuration"
  • The final instance image must have the mdadm utility
    installed and needs to be able to detect software RAID devices at boot
    time (which is usually done by having the RAID drivers embedded in the
    image’s initrd).

  • Regular cleaning will not remove RAID configuration (similarly to
    hardware RAID). To destroy RAID run the
    delete_configuration manual clean step.

  • There is no support for partition images, only whole-disk images
    are supported with Software RAID. See /install/configure-glance-images. This includes
    flavors requesting dynamic creation of swap filesystems. Swap should be
    pre-allocated inside of a disk image partition layout.

  • Images utilizing LVM for their root filesystem are not supported.
    Patches are welcome to explicitly support such functionality.

  • If the root filesystem UUID is not known to Ironic via metadata,
    then the disk image layout MUST have the first
    partition consist of the root filesystem. Ironic is agnostic if the
    partition table is a DOS MBR or a GPT partition.

    Starting in Ironic 14.0.0 (Ussuri), the root filesystem UUID can be
    set and passed through to Ironic through the Glance Image Service
    properties sub-field rootfs_uuid for the image
    to be deployed.

    Starting in Ironic 16.1.0 (Wallaby), similar functionality is
    available via the baremetal node instance_info field value
    image_rootfs_uuid. See /install/standalone for more details on standalone
    usage including an example command.

  • In UEFI mode, the Ironic Python Agent creates EFI system
    partitions (ESPs) for the bootloader and the boot configuration
    (grub.cfg or grubenv) on all holder devices. The content of these
    partitions is populated upon deployment from the deployed user image.
    Depending on how the partitions are mounted, the content of the
    partitions may get out of sync, e.g. when new kernels are installed or
    the bootloader is updated, so measures to keep these partitions in sync
    need to be taken. Note that starting with the Victoria release, the
    Ironic Python Agent configures a RAID-1 mirror for the ESPs, so no
    additional measures to ensure consistency of the ESPs should be required
    any longer.

  • In BIOS mode, the Ironic Python Agent installs the boot loader
    onto all disks. While nothing is required for kernel or grub package
    updates, re-installing the bootloader on one disk, e.g. during a disk
    replacement, may require to re-install the bootloader on all disks.
    Otherwise, there is a risk of an incompatibility of the grub components
    stored on the device (i.e. stage1/boot.img in the MBR and
    stage1.5/core.img in the MBR gap) with the ones stored in /boot
    (stage2). This incompatibility can render the node unbootable if the
    wrong disk is selected for booting.

  • Linux kernel device naming is not consistent across reboots for
    RAID devices and may be numbered in a distribution specific pattern.
    Operators will need to be mindful of this if a root device hint is
    utilized. A particular example of this is that the first “md0” device on
    a Ubuntu based ramdisk may start as device “md0”, whereas on a Centos or
    Red Hat Enterprise Linux based ramdisk may start at device “md127”.
    After a reboot, these device names may change entirely.


    Root device hints <root-device-hints> should not
    be explicitly required to utilize software RAID. Candidate devices are
    chosen by sorting the usable device list looking for the smallest usable
    device which is then sorted by name. The secondary sort by name improves
    the odds for matching the first initialized block device. In the case of
    software RAID, they are always a little smaller than the primary block
    devices due to metadata overhead, which helps make them the most likely
    candidate devices.

Image requirements

Since Ironic needs to perform additional steps when deploying nodes
with software RAID, there are some requirements the deployed images need
to fulfill. Up to and including the Train release, the image needs to
have its root file system on the first partition. Starting with Ussuri,
the image can also have additional metadata to point Ironic to the
partition with the root file system: for this, the image needs to set
the rootfs_uuid property with the file system UUID of the
root file system. One way to extract this UUID from an existing image is
to download the image, mount it as a loopback device, and use

$ sudo losetup -f
$ sudo losetup /dev/loop0 /tmp/myimage.raw
$ sudo kpartx -a /dev/loop0
$ blkid

The pre-Ussuri approach, i.e. to have the root file system on the
first partition, is kept as a fallback and hence allows software RAID
deployments where Ironic does not have access to any image metadata
(e.g. Ironic stand-alone).

Using RAID in nova
flavor for scheduling

The operator can specify the raid_level capability in nova flavor for node
to be selected for scheduling:

openstack flavor set my-baremetal-flavor --property capabilities:raid_level="1+0"

Developer documentation

In-band RAID configuration is done using IPA ramdisk. IPA ramdisk has
support for pluggable hardware managers which can be used to extend the
functionality offered by IPA ramdisk using stevedore plugins. For more
information, see Ironic Python Agent Hardware Manager <install/index.html#hardware-managers>

The hardware manager that supports RAID configuration should do the

  1. Implement a method named create_configuration. This
    method creates the RAID configuration as given in
    target_raid_config. After successful RAID configuration, it
    returns the current RAID configuration information which ironic uses to
    set node.raid_config.

  2. Implement a method named delete_configuration. This
    method deletes all the RAID disks on the bare metal.

  3. Return these two clean steps in get_clean_steps
    method with priority as 0. Example:

    return [{'step': 'create_configuration',
             'interface': 'raid',
             'priority': 0},
            {'step': 'delete_configuration',
             'interface': 'raid',
             'priority': 0}]


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