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Another way to make it transparent is using the RBD image backend in Nova
<div class="">and thus the instances look like they are running on local disk but is spawned on for</div>
<div class="">example Ceph, however that assumes you have such a backend.</div>
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<div class="">In the future, which I’ve wanted for a long time, is a images backend in Nova that simply</div>
<div class="">is a proxy to calling Cinder and getting a volume, that way it would be volumes in both cases</div>
<div class="">but that’s a lot of work and edge cases that might need to be tuned.</div>
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<div class="">On 4 Apr 2022, at 00:28, Laurent Dumont <<a href="mailto:laurentfdumont@gmail.com" class="">laurentfdumont@gmail.com</a>> wrote:</div>
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<div dir="ltr" class="">Bummer :(
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<div class="">We have a couple of use cases where I would like this to be transparent and things to automagically-unicorn and rainbows ;) Thanks for the insight Radoslaw!</div>
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<div dir="ltr" class="gmail_attr">On Sun, Apr 3, 2022 at 8:12 AM Radosław Piliszek <<a href="mailto:radoslaw.piliszek@gmail.com" class="">radoslaw.piliszek@gmail.com</a>> wrote:<br class="">
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On Sun, 3 Apr 2022 at 12:46, Laurent Dumont <<a href="mailto:laurentfdumont@gmail.com" target="_blank" class="">laurentfdumont@gmail.com</a>> wrote:<br class="">
><br class="">
> Got it!<br class="">
><br class="">
> 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)<br class="">
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I meant the filesystem quota.<br class="">
And yes, this affects config drives.<br class="">
Unfortunately, the error message from nova might be confusing.<br class="">
<br class="">
> Just to be clear on the behavior, this means that boot-from-image requests would fail?<br class="">
><br class="">
> 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.<br class="">
><br class="">
> I assume, from what I now know, that there is no mechanism to default/transform a request to BFV.<br class="">
><br class="">
> # A negative number means unlimited. Setting max_local_block_devices<br class="">
> # to 0 means that any request that attempts to create a local disk<br class="">
> # will fail. This option is meant to limit the number of local discs<br class="">
> # (so root local disc that is the result of --image being used, and<br class="">
> # any other ephemeral and swap disks). 0 does not mean that images<br class="">
> # will be automatically converted to volumes and boot instances from<br class="">
> # volumes - it just means that all requests that attempt to create a<br class="">
> # local disk will fail.<br class="">
> #<br class="">
> # Possible values:<br class="">
> #<br class="">
> # * 0: Creating a local disk is not allowed.<br class="">
> # * Negative number: Allows unlimited number of local discs.<br class="">
> # * Positive number: Allows only these many number of local discs.<br class="">
> # (Default value is 3).<br class="">
> # (integer value)<br class="">
> #max_local_block_devices = 3<br class="">
<br class="">
It seems this is actually the best approach (the error message now<br class="">
makes sense). Also confirmed by the faq -<br class="">
<a href="https://opendev.org/openstack/nova/src/commit/b0851b0e9c82446aec2ea0317514766fbc53abc0/doc/source/user/block-device-mapping.rst#faqs" rel="noreferrer" target="_blank" class="">https://opendev.org/openstack/nova/src/commit/b0851b0e9c82446aec2ea0317514766fbc53abc0/doc/source/user/block-device-mapping.rst#faqs</a><br class="">
<br class="">
-yoctozepto<br class="">
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