SSH backups - 1hr daytime; 8hrs nighttime

[John Horne]

Hi,

I posted the following message to the RedHat linux list to see if anyone had
any thoughts about this problem. I have only received a few replies, all of
which state that they have experinced poor performance problems with ssh on
Solaris. They do not, however, state if it is openssh, which version, what
hardware, or what version of Solaris. (All I can say is that we have had no
problems with openssh (2.1.1p1/2) on Solaris 7/8 with hardware from an E3000
down to an old sparc classic.)

Anyway, I wondered if anyone on this list had any ideas of what might be
causing a remote backup to take much longer overnight than during the day. I
have now run 'top' on both systems overnight and noticed nothing unusual. A
remote backup using ssh from the sparc classic to a sparcstation20,
overnight, of 1GB takes about 90mins. So 2GB would take about 3hours. Why
then does my P200 system to an Ultra 10 take over 8 hours?

Any ideas appreciated. Here's the original message:

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I've recently setup remote ssh backups from my work RH6.1 linux PC to one of
our Sun systems. The backup occurs once a week overnight. No problem with
this generally, in as much as it works (sort of) fine.

The PC is a 200Mhz system with an internal 6GB and 1 GB disk. The amount of
data being backed up is about 2GB from the 6GB disk. The Sun system is an
Ultra 10 running Solaris 8, and I'm using openSSH 2.1.1p1 on the Sun;
2.1.1p2 on the PC. Backup occurs over our local network, which may have its
problems but is generally okay.

When I was testing the setup - during the daytime - the backup took about
one hour. This was with me doing other things on the PC whilst it was going
on. Again, no problem.

I configured the backup to run overnight via cron on the PC. It was to start
at 1am. However, it took over 8 hours for the backup to complete! The
throughput from the log file shows it at about 73KB/s (from last nights
log). This takes it to about 09:30 by which time I am in work and login. I
can see the backup is still going, and when it comes to backup the final
small partition (5MB in size), it does this in a few seconds and with a
throughput of 712KB/s which is more like the throughput I get during the day!

So why is the backup taking so long? I have checked for overnight cron jobs
and disabled the cron.daily run (which kicks in at 4am). I ran top every
15mins (again via cron) overnight when the backup was not running, and could
not really see any problem. However the system did seem to be 'busy' during
the night despite no-one using the system. The %system and %nice values
seemed high (he says having now deleted the actual log file...:-( ) and
typically the system only ever got to about 60% idle. I get more than this
during the day (around 90% right now).

Anyone have any ideas about this?
--------

That's it. Thanks,

John.

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John Horne, University of Plymouth, UK             Tel: +44 (0)1752 233914
E-mail: jhorne at plymouth.ac.uk
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