[CLUE-Tech] Moving files from one system to another

[David Anselmi]

Dan Harris wrote:
> Supposedly a 63byte packet will keep it from getting "fragmented"..  at least 
> that's what I was told.

Well, -b63 is 63 blocks which is 31.5k (blocks are 512 bytes).  An IP 
packet can hold a little under 64k.  But your MTU is probably 1500 
bytes--that's the size packets get fragmented to.

Normally you don't want to send anything that exceeds the path MTU 
because you don't want routers fragmenting things.  That's better done 
on your end.  But if you just write a long stream to a socket, TCP 
should give an optimal number of packets if it knows the path MTU.  So 
I'm wondering how the writes from tar | rsh interact with TCP.

Another consideration is that tar pads files to the end of a record (63 
* 512 in this case) so performance will depend on file size.

And then there is the TCP RWIND that could be tweaked, too.

> As for the "z" flag, it actually slowed it down.  Even the fastest CPU can't 
> compress fast enough to keep the pipe flooded.  At least that was my 
> experience.

I'm not surprised though with a different cpu and bandwidth it might be 
different.  My first Internet experience was through a BBS and 
everything was compressed and delivered by 2400bps modem.  When I first 
used a Unix machine (by dial-in) it was frustrating that news and mail 
weren't compressed.  But it makes sense if you think about where the 
bottlenecks are.

Dave