How to speed up rsync when haveing lots of files

[Daniel.Li]

On Tue, 2009-03-03 at 21:26 -0700, lewis butler wrote:
> On 3-Mar-2009, at 20:33, Daniel.Li wrote:
> > On Tue, 2009-03-03 at 08:58 -0500, Charles Marcus wrote:
> >> On 3/3/2009 8:52 AM, ml at bortal.de wrote:
> >>>>> unfortunatelly rsync is beeing REALLY slow and produces a high  
> >>>>> load when
> >>>>> we try to sync lots of files (>250 000 small files).
> >>
> >>>> What version of rsync are you using?
> >>
> >>> # rsync --version
> >>> rsync  version 2.6.9  protocol version 29
> >>
> >> Upgrade to 3.0.5 (on both ends)
> >
> > OK, besides this, is there any other way to improve the network
> > performance? some thing like change the option or what?
> 
> Not so much.  a large part of 3.0 is specifically to handle large  
> numbers of files.

I found there are quit lots of options might be related with the network
performance, see bleow.

Can anyone help explain in more detail. 
e.g.
-z is apparently affect the performance when CPU has a lower frequency,
like 200MHz or so. When doing rsync, 100% cpu occupied, which limits
network performance.

BTW: I don't know more about "--compress-level=NUM", how many levels we
could use to set?

There might be others that limit/improve network performance.

So an detailed explanation is mostly appreciated. Or there might have
this kind of blog already, a link will also be OK. Thanks in advance.

--- some options that might be related to network performance---------
 -S, --sparse                handle sparse files efficiently
 -z, --compress              compress file data during the transfer
     --compress-level=NUM    explicitly set compression level
     --skip-compress=LIST    skip compressing files with a suffix in
LIST
     --bwlimit=KBPS          limit I/O bandwidth; KBytes per second
     --protocol=NUM          force an older protocol version to be used
 -4, --ipv4                  prefer IPv4
 -6, --ipv6                  prefer IPv6

> 
-- 
Daniel Li
2009.03.04