netbsd-help: Re: sluggish system response during ssh-filetransfer

Subject: Re: sluggish system response during ssh-filetransfer
To: Thomas Feddersen <thomas.feddersen@t-online.de>
From: Manuel Bouyer <bouyer@antioche.eu.org>
List: netbsd-help
Date: 10/07/2006 17:10:44

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 <bouyer@antioche.eu.org>
 NetBSD: 26 ans d'experience feront toujours la difference
--