Dear Joe,
Thanks for your kind reply, your informations are helpful. I'm reading
the imagecache.py[1] sourcecode in order to really understand what it'll
happen in case of a shared filesystem.
I understand the SHA1 hash mechanism and the backing file check but I'm
not sure how it will manage the case of shared FS.
The main function seems to be :
- backing_file = libvirt_utils.get_disk_backing_file(disk_path)
But does libvirt_utils.get_disk_backing_file federates all the compute
nodes informations ?! If no it may delete the other nodes images ?
Hope it's not too redundant,
Kind regards
[1]
https://github.com/openstack/nova/blob/master/nova/virt/libvirt/imagecache.py
Le 28/04/2015 16:18, Joe Topjian a écrit :
Hello,
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:
http://www.pixelbeat.org/docs/openstack_libvirt_images/
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.
Thanks,
Joe
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Leslie-Alexandre DENIS
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