sluggish system response during ssh-filetransfer

On Sat, Oct 07, 2006 at 03:35:48PM +0200, Thomas Feddersen
wrote:
> My server synchronizes data with another server in a
different location  
> over the internet (dsl 128kbit/sec) at regular
intervals. I use ssh to  
> tunnel through the intenet. The software used is rsync
and / or unison.  
> The server is connected to the internet over a hardware
router (ASUS  
> WL500g).
> 
> Whenever the system is actively transferring data, is
responds very  
> sluggishly to requests form the LAN: starting Midnight
Commander on the  
> server takes about 30 sec, opening an Explorer window
on a samba client  
> (WinXP or OSX) takes something between 15 sec and 60
sec. Normally either  
> of these commands are finished in just 2 sec.
> 
> The system seems not to be loaded: 'top' shows
load-averages is well below  
> 1 and an idle of over 90%. The process that does the
synchronizatiuon  
> utilizes about 1% CPU. 'systat vmstat' shows hardly any
swapping or  
> paging. 'systat iostat' shows no disk-activity beyond
the data-stream to  
> and from the interet.
> 
> I think NetBSD is supposed to be able to handle many
network-connections  
> simultaneously. Is this at all a network problem or is
maybe ssh clogging  
> something in the kernel? The server does have a
software-RAID5 array  
> (Promise IDE controller in PCIbus), but the
synchronization pertains only  
> to the drive where the NetBSD system resides (onboard
PIIXIDE).
> 
> Does anybody have an idea, how to remedy this problem?

Can you properly ping the box ? open a ssh connection ?
resolve hostnames ?

To me it looks like a DNS issue: while you're running the
transfers over
the DSL line it's overloaded, and DNS queries can take a
long time.
The solution would be to run a caching nameserver locally.

-- 
Manuel Bouyer <bouyerantioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la
difference
--