John Goerzen <jgoerzen <at> complete.org> writes:
> I've been noticing something weird here. I backed up a machine here for
> the first time. The full backup took 28 minutes. The incrementals then
> took 602 minutes, and the next one 629 minutes. Very strange, eh?
So I should add that additional testing shows that it was only the first full
backup that was fast. Every subsequent backup, whether full or incremental,
proceeded at the same very slow pace. rsync pegged at almost 100% CPU on the
machine being backed up either way.
I don't know if this is a particular feature of how BackupPC is using rsync, or
an innate part of the rsync algorithm (I will test this yet), but in any case it
would seem that using --whole-file or something could prevent the problem.
It is also possible that the first and last 128K of this file remains the same.
I should add that the backups are running over a gigabit network and that the
system being backed up is a quad-core Opteron system with 8GB RAM so we're not
talking about some old 486 in a closet or something. Further remember that the
very first full backup completed in less than half an hour, vs. 10 hours.
Thanks,
-- John
>
> I'm not using compression in my pool (compression level is 0).
>
> I discovered that the problem appears to be a 25GB file that changes
> every day. This file is a database dump. It is a binary file that
> probably differs by a GB or two each day.
>
> CPU on the server being backed up is basically 100% to rsync. Watching
> the file stream into new/ on the backuppc server, it is going through
> very slowly -- about half a MB per second. Load on the backuppc server
> is 0.01 and the CPU is 99% idle.
>
> In investigating this, I noticed that BackupPC's default rsync options
> include sending a command for a very small rsync window size -- just 2K.
> I removed that from the options but it made no difference. Next I
> tried adding --whole-file, but with that option, backuppc crashed
> immediately with "Got fatal error during xfer (fileListReceive failed)."
>
> I do not wish to do full backups on this every single night due to the
> unnecessary disk exercising, plus the unnecessary hardlink farm. What
> are my options? A 10-hour backup time on that server is unworkable (we
> backed it up to tape in under 2).
>
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