On Sun, Mar 20, 2016 at 4:08 PM, David Raison <david AT tentwentyfour DOT lu> 
wrote:
> >
>> Some more guesses:  anti-virus software slowing down access, something
>> wrong with the network connection like a full/half duplex mismatch at
>> a switch port, or not enough RAM to hold the directory tree loaded by
>> rsync forcing disk paging.
>
> I don't think a switch port or other network issue is at fault. The
> backups are run over a VPN connection which is quite stable and we're
> backing up other clients (Linux however) over the same connection
> without any trouble at all.

Switch port duplex mismatches cause intermittent problems that can be
hard to diagnose since they normally work but can drop packets when
the load is high - tcp retries cover up the problem but the connection
becomes very slow.  Long ago they were fairly common.  Back when Cisco
and Windows did not negotiate very well with each other, the common
practice was to manually configure full duplex on both sides.  Later,
the Windows box was replaced the configurations might not be kept in
sync.  If one side is manually configured it will not negotiate and
the side set to auto will have to pick half duplex.  This only happens
with managed switches and it is unlikely that you are still running
anything old enough to have the issue, but it is something relatively
simple to check if you have access to the switch.

The VPN is another possible issue if it includes any connection
timeout or equivalents to NAT gateways or statefull firewalls.  Rsync
can go for long intervals without any activity.


> Would this RAM shortage occur on the client or the server?

If either one is paging, the backup will be extremely slow.   And the
version of rsync that backuppc supports has to load the entire
directory tree in RAM before both sides start to walk it.

>>> > Notwithstanding that we need to solve the problem with the client
>>> > sending those RSTs, does anyone have any advice on how to get full runs
>>> > to not start from scratch on each run?
>> If the data is split into subdirectories, you might try adding one at
>> a time and repeating the runs as they complete.
>
>
> Would you do this by adding to $Conf{BackupFilesOnly} after each
> successful run or by gradually extending $Conf{RsyncShareName} ?
>

I think I'd try adding a top level directory at a time to
$Conf{BackupFilesOnly}, starting with something small if possible.
That should let you get an idea of what kind of speed you are getting
before hitting whatever is causing your failures.

-- 
   Les Mikesell
     lesmikesell AT gmail DOT com

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