[Openstack-operators] [openstack][nova] Several questions/experiences about _base directory on a big production environment

Diego Parrilla Santamaría diego.parrilla.santamaria at gmail.com
Wed Apr 2 18:26:18 UTC 2014

Dear Alejandro,

every time we run a script to prune the _base directory in our enviroments
we raise a pray to Santa Bárbara (
http://es.wikipedia.org/wiki/B%C3%A1rbara_(m%C3%A1rtir)#Patronazgo). Yes,
_base folder with shared storage is a risky business.

Have you considered not using _base backed images? This article can help:

If I'm right and you are using some kind of NFS device with deduplication,
may be it can be an option.


Diego Parrilla
*www.stackops.com <http://www.stackops.com/> | * diego.parrilla at stackops.com |
+34 91 005-2164 | skype:diegoparrilla

On Wed, Apr 2, 2014 at 8:04 PM, Alejandro Comisario <
alejandro.comisario at mercadolibre.com> wrote:

> Hi guys ...
> We have a pretty big openstack environment and we use a shared NFS to
> populate backing file directory ( the famous _base directory located
> on /var/lib/nova/instances/_base ) due to a human error, the backing
> file used by thousands of guests was deleted, causing this guests to
> go read-only filesystem in a second.
> Till that moment we were convinced to use the _base directory as a
> shared NFS because:
> * spawning a new ami gives total visibility to the whole cloud making
> instances take nothing to boot despite the nova region
> * ease glance workload
> * easiest management no having to replicate files constantly not
> pushing bandwidth usage internally
> But after this really big issue, and after what took us to recover
> from this, we were thinking about how to protect against this kind of
> "single point of failure".
> Our first aproach this days was to put Read Only the NFS share, making
> impossible for computes ( and humans ) to write to that directory,
> giving permision to just one compute whos the one responsible to spawn
> an instance from a new ami and write the file to the directory, still
> ... the storage keeps being the SPOF.
> So, we are handling the possibility of having the used backing files
> LOCAL on every compute ( +1K hosts ) and reduce the failure chances to
> the minimum, obviously, with a pararell talk about what technology to
> use to keep data replicated among computes when a new ami is launched,
> launching times, performance matters on compute nodes having to store
> backing files locally, etc.
> This make me realize, i have a huge comminity behind openstack, so
> wanted to ear from it:
> * what are your thoughts about what happened / what we are thinking right
> now ?
> * how does other users manage the backing file ( _base ) directory
> having all this considerations on big openstack deployments ?
> I will be thrilled to read from other users, experiences and thoughts.
> As allways, best.
> Alejandro
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