Julia Kreger 454ad95666 Update RAID docs

I've been asked a number of questions w/r/t RAID recently, and
thoguht it would be easiest to just update the documentation for
the purposes of clarity.

Change-Id: I940d4a625ac635a6e4c374a6e3e5e5228a6f8a77

2021-12-15 10:04:32 -08:00

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RAID Configuration

Overview

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 the REST API reference for their corresponding REST API requests.

Prerequisites

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 RAID 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 interface.

Build 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.

Note

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.

RAID configuration JSON format

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 like:

{
  "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 auto-generated.
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_type - hdd or ssd. If this is not specified, disk type will not be a criterion to find backing physical disks.
interface_type - sata 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 software.
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 necessary).

Note

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 `target_raid_config`

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 image:

{
  "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": [
        "Disk.Bay.0:Encl.Int.0-1:RAID.Integrated.1-1",
        "Disk.Bay.1:Encl.Int.0-1:RAID.Integrated.1-1"
      ]
    },
    {
      "size_gb": 100,
      "raid_level": "5",
      "controller": "RAID.Integrated.1-1",
      "volume_name": "data_volume",
      "physical_disks": [
        "Disk.Bay.2:Encl.Int.0-1:RAID.Integrated.1-1",
        "Disk.Bay.3:Encl.Int.0-1:RAID.Integrated.1-1",
        "Disk.Bay.4:Encl.Int.0-1:RAID.Integrated.1-1"
      ]
    }
  ]
}

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>

Workflow

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 information.
Operator prepares the desired target RAID configuration as mentioned in Target RAID configuration. The target RAID configuration is set on the Ironic node:
```
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"
}]
```
Note

'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.

Note

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 blkid:

$ 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> documentation.

The hardware manager that supports RAID configuration should do the following:

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

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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