On Tue, Oct 28, 2014 at 9:27 AM, Dan Genin <daniel.ge...@jhuapl.edu> wrote:

>  So this brings us back to the original proposal of having separate
> backing files for Cinder and Nova which Dean thought might take too much
> space.

Between Cinder, Nova and Swift (and Ceph, etc) everybody wants some
loopback disk images.  DevStack's Swift and Ceph configurations assume
loopback devices and do no sharing.

> Duncan, could you please elaborate on the pain a single volume group is
> likely to cause for Cinder? Is it a show stopper?

Back in the day, DevStack was built to configure Cinder (and Nova Volume
before that) to use a specific existing volume group (VOLUME_GROUP_NAME) or
create a loopback file if necessary.  With the help of VOLUME_NAME_PREFIX
and volume_name_template DevStack knew which logical volumes belong to
Cinder and could Do The Right Thing.

With three loopback files being created, all wanting larger and larger
defaults, adding a fourth becomes Just One More Thing.  If Nova's use of
LVM is similar enough to Cinder's (uses deterministic naming for the LVs)
I'm betting we could make it work.



Dean Troyer
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