---------- Forwarded message ----------
From: Sean Clark <smclark AT tamu DOT edu>
Date: Thu, Jan 20, 2011 at 10:41 AM
Subject: Re: [Bacula-users] Very low performance with compression and
encryption !
To: John Drescher <drescherjm AT gmail DOT com>


On 01/20/2011 09:00 AM, John Drescher wrote:
> This is normal. If you want fast compression do not use software
> compression and use a tape drive with HW compression like LTO drives.
>
> John
Not really an option for file/disk devices though.

I've been tempted to experiment with BTRFS using LZO or standard zlib
compression for storing the volumes and see how the performance compares
to having bacula-fd do the compression before sending - I have a
suspicion the former might be better..

For the original question though - not only is this normal, this is
normal for programs other than bacula.  I see the same thing happen when
using compression with scp/ssh (and even "tar -cf - | gzip | nc" ) as
well, for example.  The latency introduced by pausing to compress the
data into each packet unavoidably slows things down, and compression is
really only useful over very slow links (or in bacula's case, only if
you're more worried about disk space than backup speed.)

LZO is a faster, apparently much less cpu-intensive algorithm (though it
does not compress as well as zlib) - it might be that if bacula-fd had
an LZO compression option better throughput might be possible while
still getting some space savings.  Even so, looking into some method of
storage-side compression is likely to give you better performance in my
experience.



-- 
John M. Drescher

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