On Thu, Oct 16, 2014 at 7:25 AM, Sorin Srbu <Sorin.Srbu AT orgfarm.uu DOT se> 
wrote:
>
> I'm seeing network speeds at about 35-45 Mbps when using BackupPC and rsync 
> over ssh.
>

That sounds pretty good.  But unless you have a lot of new files
created daily, the bottleneck is usually disk speed, especially
merging a lot of small changes into a big existing file.

> Running iperf below I notice the network should theoretically be capable of a 
> bit more than that. I understand that ssh adds quite a bit of bottleneck.

There is some overhead for encryption.  Back when cpus were slow
enough for it to matter I used to set blowfish as the preferred
cipher.  Now you probably want aes-128 where you have hardware
support.

>
> After reading one of the answers at 
> <<http://serverfault.com/questions/377598/why-is-my-rsync-so-slow>>, I kinda' 
> wonder if the NFS-angle would work for use with BackupPC and how I would go 
> about it. Is the tar transfer method the only one supported by BPC if using 
> NFS for example?
> Rsyncing a NFS-mounted remote host supposedly is a lot faster than doing 
> rsync over ssh.
>
> Any thoughts on this?

I'd guess there are too many variables to predict but I'd stick to ssh
because of the forced validation (--ignore-times) on full runs.  In
the case that will ultimately matter the most (the third and
subsequent full runs)  you can avoid most of the server-side reads if
you used checksum caching but you still have to perform a full read of
the content on the client side.  With ssh, that's a local disk access.
with nfs you'll copy every file across the network just so rsync can
compute its block checksum even where everything already matches.

-- 
   Les Mikesell
     lesmikesell AT gmail DOT com

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