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Re: [dm-devel] [Multipath] Round-robin performance limit

On Thu, Dec 22, 2011 at 07:54:46PM -0500, John A. Sullivan III wrote:
> On Wed, 2011-10-05 at 15:54 -0400, Adam Chasen wrote:
> > John,
> > I am limited in a similar fashion. I would much prefer to use multibus
> > multipath, but was unable to achieve bandwidth which would exceed a
> > single link even though it was spread over the 4 available links. Were
> > you able to gain even a similar performance of the RAID0 setup with
> > the multibus multipath?
> > 
> > Thanks,
> > Adam
> <snip>
> We just ran a quick benchmark before optimizing.  Using multibus rather
> than RAID0 with four GbE NICs, and testing with a simple cat /dev/zero >
> zeros, we hit 3.664 Gbps!
> This is still on CentOS 5.4 so we are not able to play with
> rr_min_io_rq.  We have not yet activated jumbo frames. We are also
> thinking of using SFQ as a qdisc instead of the default pfifo_fast.  So,
> we think we can make it go even faster.
> We are delighted to be achieving this with multibus rather than RAID0 as
> it means we can take transactionally consistent snapshots on the SAN.
> Many thanks to whomever pointed out that tag queueing should solve the
> 4KB block size latency problem.  The problem turned out to not be
> latency as we were told but simply an under resources SAN.  We brought
> in new Nexenta SANs with much more RAM and they are flying - John


Can you please post your multipath configuration ? 
Just for reference for future people googling for this :)

-- Pasi

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