[X-Unix] Re: Pokey LAN transfers (Resolved)

[David Ledger]

At 22:16 -0500 27/12/07, TjL wrote:
>On 12/27/07, Richard Hartman <seasoft at west.net> wrote:
>>  - Unmounting the LAN volume and instead using scp or rsync (and the
>>  IP address of the source mac) produced the expected transfer rate of
>>  100 megabits/sec, which was the speed limit expected by the slowest
>>  network element in the loop (the 100 mbps nic on one of the macs).
>Someone else had suggested FTP.  Would it work similarly well?
>
>I don't know much about this, but it would seem to me that scp would
>be slower if there's encryption going on.  rsync would, I assume, be
>faster than scp, but would rsync and ftp be comparable?

scp does have the encryption overhead. CPUs are fast, but encryption 
will be a measurable overhead for a 1Gbps network connection. The 
network handles data one bit at a time. The encryption works on 32 or 
64 bits at a time at a clock speed of up to about twice that of the 
network. Any processing taking more than 64 or 128 clock cycles per 
32 or 64 bit chunk will slow the transfer - not even considering all 
the other extra systemy things that including that processing will 
add.

rsync uses extra network traffic to find out what is already at the 
destination.

The only extra that FTP requires is the normal TCP validation etc. 
It's the transfer protocol that gets closest to raw network speed and 
is used to test network throughput.

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