Support to allow only boot from cinder volumes

Radosław Piliszek radoslaw.piliszek at
Sun Apr 3 12:12:47 UTC 2022

On Sun, 3 Apr 2022 at 12:46, Laurent Dumont <laurentfdumont at> wrote:
> Got it!
> By quota, do you mean reserved_host_disk_mb in nova.conf? I could make the /var/lib/nova/instances RO but I am not sure how that would impact config drive that are created locally (since I dont have ceph)

I meant the filesystem quota.
And yes, this affects config drives.
Unfortunately, the error message from nova might be confusing.

> Just to be clear on the behavior, this means that boot-from-image requests would fail?
> Looking at nova.conf, I can disable the number of local-disks supported, but this doesn't act as a behavior change when the requests are made.
> I assume, from what I now know, that there is no mechanism to default/transform a request to BFV.
> # A negative number means unlimited. Setting max_local_block_devices
> # to 0 means that any request that attempts to create a local disk
> # will fail. This option is meant to limit the number of local discs
> # (so root local disc that is the result of --image being used, and
> # any other ephemeral and swap disks). 0 does not mean that images
> # will be automatically converted to volumes and boot instances from
> # volumes - it just means that all requests that attempt to create a
> # local disk will fail.
> #
> # Possible values:
> #
> # * 0: Creating a local disk is not allowed.
> # * Negative number: Allows unlimited number of local discs.
> # * Positive number: Allows only these many number of local discs.
> #                        (Default value is 3).
> #  (integer value)
> #max_local_block_devices = 3

It seems this is actually the best approach (the error message now
makes sense). Also confirmed by the faq -


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