[openstack-dev] [Nova] Default ephemeral filesystem

Daniel P. Berrange berrange at redhat.com
Fri Dec 20 10:00:07 UTC 2013

On Fri, Dec 20, 2013 at 09:21:54AM +1300, Robert Collins wrote:
> The default ephemeral filesystem in Nova is ext3 (for Linux). However
> ext3 is IMNSHO a pretty poor choice given ext4's existence. I can
> totally accept that other fs's like xfs might be contentious - but is
> there any reason not to make ext4 the default?
> I'm not aware of any distro that doesn't have ext4 support - even RHEL
> defaults to ext4 in RHEL5.
> The reason I'm raising this is that making a 1TB ext3 ephemeral volume
> does (way) over 5GB of writes due to zeroing all the inode tables, but
> an ext4 one does less than 1% of the IO - 14m vs 7seconds in my brief
> testing. (We were investigating why baremetal deploys were slow :)).

I've no objection to changing the default in this way. I would suggest
though that we make the hoice of emphemeral filesystem configurable
per-instance. I can well imagine people wanting to be able to choose
xfs or btrfs instead of ext4.

My suggestion would be to support a glance image metadata property to
let users specify the filesystem that is suitable for use with their

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