From mboxrd@z Thu Jan  1 00:00:00 1970
From: Josh Durgin <josh.durgin@inktank.com>
Subject: Re: write-through cache
Date: Wed, 23 May 2012 17:44:11 -0700
Message-ID: <4FBD845B.5030402@inktank.com>
References: <CA+jddaPW1YpHqo667dD6_9ce8iRhQLOX911-dWKT+XRFMR3YGw@mail.gmail.com>
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To: Mandell Degerness <mandell@pistoncloud.com>
Cc: ceph-devel@vger.kernel.org

On 05/23/2012 04:44 PM, Mandell Degerness wrote:
> I would like to test the effect of using the new write-through cache
> on RBD volumes mounted to Openstack VMs.  What, precisely, are the
> changes I need to make to the volume XML in order to do so?

If your only volumes are rbd, you can append 
:rbd_cache=true:rbd_cache_max_dirty=0 to the image name in the volume 
xml, so it would include something like

<source protocol="rbd" 
name="pool/image:rbd_cache=true:rbd_cache_max_dirty=0">

Josh