[X-Unix] Pokey LAN transfers

[David Ledger]

>On Dec 26, 2007, at 3:54 PM, Richard Hartman wrote:
>>  I'm looking for guidance on how best to copy large data sets 
>>between macs on a network (Finder, terminal cp, other?).
>>  The setup: Copying from mac #1 (a 2006 iMac running 10.4.11 with 
>>built-in 100bps ethernet) to mac #2 (a recent PBPro running 10.5.1 
>>with built-in Gigabit ethernet). Macs connected by a Gigabit 
>>netgear switch.
>>  I had hoped to get sustained transfers between these two macs of 
>>50-70 mbps (throttled by the rate-limiting 100 mbps iMac 
>>capability).
>>  However, copying a single 2 GByte file, by mounting the (Tiger) 
>>imac on the (Leopard) MBPro desktop and using terminal "cp" command 
>>from the MBPro terminal, results in a sustained transfer rate of 
>>only about 2.5 mB/sec (25 mbps).
>>  So, the questions:
>>  - Is this rather low transfer rate normal for my setup?
>>  - Might I improve it using other tools?

If Resource forks are not a problem, you'll get fastest throughput 
with standard command line FTP. It's no bells/whistles but makes best 
use of the network.

At 17:53 -0600 26/12/07, Nick Scalise wrote:
>Do you have your network cards locked in at their rated speeds? It 
>could be that they are not negotiating with the Gig switch properly.
>For the 100Mbps Mac, locked at '100MB/Full duplex' and the Gigabit 
>Mac locked at '1G/Full?'

That would mean that the switch has to either buffer up a full MTU 
length coming in at 100Mbps and then squirt it out at 1Gbps for 
packets going one way, or buffer a buffer up packets coming in at 
1Gbps and clock the bits out at 100Mbps. If the switch is very quick 
doing this it will work well, but for domestic switches it may well 
add extra delay. Much better to set both to 100Mbps and let the 
switch just pass it all through.

The MTU (Maximum Transmission Unit) must be the same on both 
computers. Unless you've changed it it will be the normal default of 
1500 for wired connections. If you want to check it, see
<http://docs.info.apple.com/article.html?artnum=303192>
It is the maximum packet size, and, if different, the packets will 
have to be buffered up and split into packets of the other size at 
some point, probably in the switch if it's also a router.

David


-- 
David Ledger - Freelance Unix Sysadmin in the UK.
HP-UX specialist of hpUG technical user group (www.hpug.org.uk)
david.ledger at ivdcs.co.uk
www.ivdcs.co.uk