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On 20 September 2016 at 16:24, Nikita Konovalov <nkonovalov at mirantis.com>
wrote:

> Hi,
>
> From Sahara (and Hadoop workload in general) use-case the reason we used
> BDD was a complete absence of any overhead on compute resources
> utilization.
>
> The results show that the LVM+Local target perform pretty close to BDD in
> synthetic tests. It's a good sign for LVM. It actually shows that most of
> the storage virtualization overhead is not caused by LVM partitions and
> drivers themselves but rather by the iSCSI daemons.
>
> So I would still like to have the ability to attach partitions locally
> bypassing the iSCSI to guarantee 2 things:
> * Make sure that lio processes do not compete for CPU and RAM with VMs
> running on the same host.
> * Make sure that CPU intensive VMs (or whatever else is running nearby)
> are not blocking the storage.
>

So these are, unless we see the effects via benchmarks, completely
meaningless requirements. Ivan's initial benchmarks suggest that LVM+LIO is
pretty much close enough to BDD even with iSCSI involved. If you're aware
of a case where it isn't, the first thing to do is to provide proof via a
reproducible benchmark. Otherwise we are likely to proceed, as John
suggests, with the assumption that local target does not provide much
benefit.

I've a few benchmarks myself that I suspect will find areas where getting
rid of iSCSI is benefit, however if you have any then you really need to
step up and provide the evidence. Relying on vague claims of overhead is
now proven to not be a good idea.
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