[Rdo-list] introspection and raid configuration

Dmitry Tantsur dtantsur at redhat.com
Wed May 27 07:50:46 UTC 2015

On 05/27/2015 09:38 AM, Imre Farkas wrote:
> On 05/26/2015 05:43 PM, Dmitry Tantsur wrote:
>> On 05/26/2015 04:42 PM, Imre Farkas wrote:
>>> Hi all,
>>> I would like to gather some feedback on the current worfklow regarding
>>> the subject. RAID configuration on DRAC machines works as follows (it
>>> assumes there's no RAID volume on the machine):
>>> 1. user defines the deployment profile and the target raid configuration
>>> for each profile
>>> 2. ironic-discoverd introspects the node to gather facts
>>> 3. ach-match picks a deployment profile based on the gathered facts
>>> 4. instack triggers the raid configuration based on the selected profile
>>> A bug[1] has been discovered regarding step 2: ironic-discoverd fails
>>> because it tries to figure out the size of the local disk but it can't
>>> find any as no volume exists on the RAID controller yet. This is a
>>> chicken-and-egg problem because ironic-discoverd doesn't work if the
>>> RAID volume(s) has not been configured but the RAID configuration can't
>>> be triggered if ironic-discoverd hasn't gathered the facts about the
>>> node.
>>> Few possible workarounds:
>>> #1: make saving the local disk size optional in the standard plugin in
>>> ironic-discoverd. The downside is that the standard plugin is supposed
>>> to enroll nodes in ironic with all attributes necessary for scheduling.
>>> This assumption might fail with this solution.
>> -1 will never get upstream for the reasons you stated
>>> #2: run discovery multiple times with different set of plugins. The run
>>> before RAID configuration would exclude the standard plugin while the
>>> run afterwards could potentially exclude others. The parameters passed
>>> by the user to ironic-discoverd for each run need to be properly
>>> documented. It would slow down the installation because each run
>>> requires a reboot which takes a lot of time on bare metal.
>> Possible, but better (IMO) idea below.
>>> #3: name your suggestion!
>> #3. modify your existing root_device_hint plugin to insert a fake
>> local_gb value (with issuing a warning), and then put it to the
>> beginning of the plugin pipeline. WDYT?
> I would avoid that for the very same reason as we rejected option #1: it
> would do things quite differently than it is expected. However, building
> on top of this idea, we could introduce a fake_local_gb plugin and
> enable it as default in instack. Thoughts?


I would say it's fine for root_device_hint plugin. It's not enabled by 
default upstream, and it's a normal flow involving it.

> Imre
>>> Any thoughts/preference on the above described workarounds?
>>> Thanks,
>>> Imre
>>> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1222124

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