On 27/11/14 07:27, Christian Völker wrote:
> Hi,
>
> I assume this has been discussed several times but I did not find any
> real comparisation of numbers.
>
> So just to ask if anybody has some experience with the two major
> transfer methods (rsync/ssh or rsyncd)?
>
> By default rsyncd will be faster as otherwise we have the ssh overhead,
> correct?
>
> But I can enable compression for ssh while compression for the
> perl-rsync used by BackupPC does not work.
>
> So what is faster on a slow line of approx 10Mbit? ssh with compression
> to max or sync without compression. And of course, it depends by the
> data to be transfered. Assume mostly binary files.
>
Well, it depends is the short answer, your environment will be different
to mine, so you should test and measure and then decide. However, that
can be a time consuming option, so think about the various aspects that
can impact the speeds, and then you can make a guesstimate to which path
you want to start on. If it doesn't provide the performance you need,
then you can investigate the other option just to check.
So, it depends on how much data rsync will want to transfer, and how
much time it will spend actually trying to transfer that data. eg, if
your source has 500G of data, but only 500MB changes per day, then rsync
will need to transfer 500MB. If the changed data is spread evenly over
all files in the source, then rsync will spend time finding the
differences in each file, and a small amount of time actually
transferring those changes. OTOH, if the 500MB changes are all within 1%
of the files, then rsync will spend time verifying that the other files
haven't changed (quick), and lots of time waiting for the portions of
the changed files to transfer. In this case, compression might help you.
However, compressing data will increase your CPU requirement, and rsync
already requires CPU in order to calculate differences/etc, so if you
don't have enough spare CPU to compress at more than 10Mbps, (ie,
compress more than 10Mbps of uncompressed data, even if the output of
the compression is still less than 10Mbps) then compression isn't useful.
Finally, if you have a 10Mbps line, don't expect to see it 100% utilised
during the backup period anyway, between rsync spending time looking for
differences, disk IO at both ends, etc, there are many other factors to
consider.
Hope that gives you some things to think about.
Regards,
Adam
--
Adam Goryachev Website Managers www.websitemanagers.com.au
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