[plug] ADSL modem dropout while doing an rsync backup

[Steve Boak]

On Mon, 15 Sep 2008 02:58:39 pm Daniel Pittman wrote:
> Steve Boak <sboak at westnet.com.au> writes:
> > I am having a weird problem with an ADSL connection - every time I try
> > to do an rsync backup over the internet, the modem drops out and
> > reconnects repeatedly every minute or so thereafter until it is hard
> > reset by turning the modem power off and on again.
> >
> > The backup script is a cron job on a remote machine, pulling data off
> > the local server and storing it off-site at 3am every morning. Within
> > one minute of the backup job starting, the modem on the local server
> > has a hernia, and continues cycling until it is reset.
> >
> > There are no errors in the server logs, other than those caused by the
> > network connection being down. It appears that compressed rsync data
> > is upsetting the modem, but firstly that seems unlikely, and secondly
> > I can't find any reference to anyone else having a similar problem.
>
> It is pretty unlikely that the modem is upset by the rsync traffic
> specifically, since it is encrypted by ssh and will look *different*
> every time it flows past.
>
> > Westnet log the fact that the connection has been lost and
> > re-established, but nothing except the generic 'port error'. They are
> > not much help after I mention the words "Linux" and "rsync"... :-)
>
> [...]
>
> > The problem still exists, but I've stopped using this method of backup
> > until I resolve this strange issue.
> >
> > Any ideas?
>
> At a guess, you have a load related bug, which the rsync transfer
> triggers by being a high enough load for long enough.
>
> Possible causes: a firmware bug in the modem; try updating.  A marginal
> connection; try selecting a less aggressive ADSL mode, if your provider
> offers that.  Overheating of the modem; check what temperature it gets
> to.

Line connection should be good, only a stone's throw from the exchange (I 
know, that doesn't guarantee a good connection...)

Modem doesn't _feel_ hot normally, but it may be when under high load. I don't 
know if it has a temperature sensor on board that I can read. I'll try 
software updates next week when I get back on site, and if that doesn't work 
I can try swapping the modem for one of a different brand which I just happen 
to have spare at the moment.

> You might also validate the theory by using something else that will
> transfer a similar volume of data at a similar rate, then see if you get
> the same drop-out.
>
> Regards,
>         Daniel

I'll try that too, and Nick's suggestion of the "--bwlimit" option.

In fact, I'll try these suggestions BEFORE I do a software update on the 
modem, just because I really would like to know what is happening and why :-)

Ta

Steve


-- 
Steve Boak, (08) 9756 0662, P.O. Box 240, Nannup, WA 6275
Nannup Telecentre IT Support, Phone (08) 9756 3022
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