Re: dm-multipath has great throughput but we'd like more!

[Jonathan E Brassow <jbrassow@redhat.com>]

The system bus isn't a limiting factor is it?  64-bit PCI-X will get 
8.5 GB/s (plenty), but 32-bit PCI 33MHz got 133MB/s.

Can your disks sustain that much bandwidth? 10 striped drives might get 
better than 200MB/s if done right, I suppose.

Don't the switches run at 2 Gbits/s?  2 Gbits/s / 10 (throw in 2 bits 
for protocol) ~= 200MB/s.

Could be a bunch of reasons...

  brassow

On May 18, 2006, at 2:05 AM, Bob Gautier wrote:

> Yesterday my client was testing of multipath load balancing and 
> failover
> on a system running ext3 on a logical volume which comprises about ten
> SAN LUNs all reached using multipath in multibus mode over two QL2340
> HBAs.
>
> On the one hand, the client is very impressed: running bonnie++
> (inspired by Ronan's GFS v VxFS example) we get just over 200Mbyte/s
> over the two HBAs, and when we pull a link we get about 120MByte/s.
>
> The throughput and failover response times are better than the client
> has ever seen, but we're wondering why we are not seeing higher
> throughput per-HBA -- the QL2340 datasheet says it should manage
> 200Mbyte/s and all switches etc. run at 2GBps.
>
> Any ideas?
>
> Bob Gautier
> +44 7921 700996
>
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