[Openstack-operators] [Openstack] [nova] Cleaning up unused images in the cache

Joe Topjian joe at topjian.net
Tue Apr 28 14:18:53 UTC 2015


I've got a similar question about cache-manager and the presence of a
> shared filesystem for instances images.
> I'm currently reading the source code in order to find out how this is
> managed but before I would be curious how you achieve this on production
> servers.
> For example images not used by compute node A will probably be cleaned on
> the shared FS despite the fact that compute B use it, that's the main
> problem.

This used to be a problem, but AFAIK it should not happen any more. If
you're noticing it happening, please raise a flag.

> How do you handle _base guys ?

We configure Nova to not have instances rely on _base files. We found it to
be too dangerous of a single point of failure. For example, we ran into the
scenario you described a few years ago before it was fixed. Bugs are one
thing, but there are a lot of other ways a _base file can become corrupt or
removed. Even if those scenarios are rare, the results are damaging enough
for us to totally forgo reliance of _base files.

Padraig Brady has an awesome article that details the many ways you can
configure _base and instance files:


I'm looping -operators into this thread for input on further ways to handle
_base. You might also be able to find some other methods by searching the
-operators mailing list archive.

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