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Re: [SOLVED]Re: Only 8 MB/sec write throughput with NetBSD 5.1 AMD64

On Sun, Oct 09, 2011 at 12:19:59PM -0700, Tony Bourke wrote:
> changing MTU won't help really.

Do you have data on which to base this conclusioN?

> it would also cause lots of other problems (like fragmentation over your
> Internet connection)

No.  That is what path MTU discovery is for.

> and every device on your deity would need to be set for the same MTU.

I am not sure what deity is involved with this, except perhaps for the god
of unclear thinking (how many times have I tried to get him out of my
personal pantheon? it's not working)

> Plus you should be able to push way more bandwidth without it.

With a laptop disk drive as the data sink?

> higher MTUs used to be a way to increase performance for things like
> iSCSI but that's not really the case anymore, even with 10 Gigabit
> Ethernet. So even 10 gigabit environments choose not to do jumbo frames. 

If you say so.  Actually, network adapters got smart enough to make little
packets look like big packets to the OS (segmentation offload on send,
"Large Receive" on receive) but since we don't know what "Dlink Gigabit
adapter" is in use here, I have to question whether the former hardware
optimization is in use, and I can be sure the latter is not since NetBSD
does not presently support it with any network adapter.

> If your network card is PCI, your bandwidth will be limited to about
> 200-250 megabits per second (which is about 25-35 MBytes/s) because
> of the bus speed.

The claim is false.  Even giving a conservative 80MByte/sec estimate for
33MHz 32-bit PCI (the theoretical maximum is 132MByte/sec), and allowing
for some adapter overhead, that's well north of 500 megabits per second
-- and, in fact, 400-500 megabits per second can easily be achieved with
such adapters, under NetBSD.  Clearly, either 64 bit or 66MHz PCI (never
mind 64 bit, 133Mhz PCI-X) is sufficient to fill a gigabit link or come
very, very close (and indeed it is easy to reproduce this result with
real hardware under NetBSD as well).

> PCIe will handle full duplex 1 gigabit no problem.

The claim is true.


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