[openstack-dev] [nova][cinder] Limits on volume read throughput?

Preston L. Bannister preston at bannister.us
Mon Mar 7 06:25:12 UTC 2016

Should add that the physical host of the moment is Centos 7 with a
packstack install of OpenStack. The instance is Ubuntu Trusty. Centos 7 has
a relatively old 3.10 Linux kernel.

>From the last week (or so) of digging, I found there were substantial
claimed improvements in *both* flash support in Linux and the block I/O
path in QEMU - in more recent versions. How much that impacts the current
measures, I do not (yet) know.

Which suggests a bit of tension. Redhat folk are behind much of these
improvements, but RHEL (and Centos) are rather far behind. Existing RHEL
customers want and need careful, conservative changes. Folk deploying
OpenStack need more aggressive release content, for which Ubuntu is
currently the best base.

Will we see a "Redhat Cloud Base" as an offering with RHEL support levels,
and more aggressive QEMU and Linux kernel inclusion?

At least for now, building OpenStack clouds on Ubuntu might be a much
better bet.

Are those claimed improvements in QEMU and the Linux kernel going to make a
difference in my measured result? I do not know. Still reading, building
tests, and collecting measures...

On Thu, Mar 3, 2016 at 11:28 AM, Chris Friesen <chris.friesen at windriver.com>

> On 03/03/2016 01:13 PM, Preston L. Bannister wrote:
>     > Scanning the same volume from within the instance still gets the same
>>     > ~450MB/s that I saw before.
>>     Hmmm, with iSCSI inbetween that could be the TCP memcpy limitation.
>> Measuring iSCSI in isolation is next on my list. Both on the physical
>> host, and
>> in the instance. (Now to find that link to the iSCSI test, again...)
> Based on earlier comments it appears that you're using the qemu built-in
> iSCSI initiator.
> Assuming that's the case, maybe it would make sense to do a test run with
> the in-kernel iSCSI code and take qemu out of the picture?
> Chris
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