openstack
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ironic
Code Issues Proposed changes

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
This commit is contained in:
Julia Kreger 2021-12-14 15:50:53 -08:00
parent 0aea12247e
commit 454ad95666
1 changed files with 41 additions and 4 deletions
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45
doc/source/admin/raid.rst
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@ -389,16 +389,35 @@ There are certain limitations to be aware of:
"step": "create_configuration"
}]
* If local boot is going to be used, 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).
* 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 :doc:`/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 :doc:`/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
@ -420,6 +439,24 @@ There are certain limitations to be aware of:
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::
:ref:`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
------------------