[dm-devel] dm-multipath has great throughput but we'd like more!

[Jonathan E Brassow]

On May 18, 2006, at 2:44 AM, Bob Gautier wrote:

> On Thu, 2006-05-18 at 02:25 -0500, Jonathan E Brassow wrote:
>> 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.
>>
>
> Thanks for the fast responses:
>
> The card is a 64-bit PCI-X, so I don't think the bus is the bottleneck,
> and anyway the vendor specifies a maximum throughput of 200Mbyte/s per
> card.
>
> The disk array does not appear to be the bottleneck because we get
> 200Mbyte/s when we use *two* HBAs in load-balanced mode.
>
> The question is really about why we only see O(100Mbyte/s) with one HBA
> when we can achieve O(200MByte/s) with two cards, given that one card
> should be able to achieve that throughput.
>
> I don't think the method of producing the traffic (bonnie++ or 
> something
> else) should be relevant but if it were that would be very interesting
> for the benchmark authors!
>
> The storage is an HDS 9980 (I think?)
>

I guess I was thinking you were asking why you weren't getting 240MB/s, 
and I overlooked the obvious question.  I guess I don't know the answer 
(or even the right questions).  :(

  brassow