[plug] ADSL modem dropout while doing an rsync backup

[Daniel Pittman]

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.

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