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





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


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