Efficiency of remote copy

[Mark . Burgess]

Daniel,

I tried to reproduce some numbers to check how cfengine copying
was in relation to other tools. I don't have rsync set up here, so the
closest I got to your test was scp: The results on 500MB were

SCP --

real    22m10.360s  (plus-minus 15sec)
user    0m34.320s
sys     0m14.180s

daneel# time /local/sbin/cfagent -K -f cftest

real    20m26.420s (plus minus 15 sec)
user    1m11.800s
sys     0m23.570s


This is not a huge difference, so I cannot se that anything is
actually wrong. I don't fully understand why cfagent/cfservd don't work
up more of a sweat and make things go faster. Possibly network
is the bottleneck. I'm afraid I don't have any appropriate tools
(or time) to try to evaluate the efficiency at the moment, but
I would be interested to know of anyone who does and could do this --
e.g. using some tool like a code analyzer to find out where
programs are spending most of their time. Looking at resource
usgae in detail on both hosts.

This would be a good exercise -- perhpas a paper for LISA 2003?

cheers,
Mark



On  6 Jul, Daniel Riek wrote:
> Ha Mark,
> 
> I can't say anything on the general performance but in our case, it
> looks like this:
> 
> Cfengine config:
> [...]
>       www.!www1.do_mirror_test::
>               /usr/local/sourcedir
>               dest=/opt/mirror_test
>               syslog=false
>               encrypt=false
>               purge=true
>               timestamps=preserv
>               type=ctime
>               backup=false
>               recurse=inf
>               trustkey=true
>               server=www1.mydomain
> [...]
> 
> 
> - First run without existing dest dir:
> 
> [root@www2 root]# time cfagent -K -D do_mirror_test
> real    8m52.785s
> user    0m1.270s
> sys     0m12.810s
> 
> Ah, one more thing, the first data in my mail to Adrian was with
> "syslog=true". - So without logging it looks much better...
> 
> - Second run with unchanged source dir:
> 
> [root@wwww2 root]# time cfagent -K -D do_mirror_test
> 
> real    7m20.412s
> user    0m0.430s
> sys     0m0.120s
> 
> And now RSync:
> 
> Firstrun with nonexisting dest dir:
> [root@www2 opt]# time rsync -az -e ssh root@www1:/usr/local/sourcedir 
> mirror_test
> 
> real    3m43.060s
> user    0m37.400s
> sys     0m12.590s
> 
> 
> And unchanged sourcedir:
> [root@www2 opt]# time rsync -az -e ssh root@www1:/usr/local/sourcedir 
> mirror_test
> 
> real    0m1.404s
> user    0m0.610s
> sys     0m0.240s
> 
> 
> To be correct, we have to take into account, that cfengine is doing more
> than just copying that dir. So cfagent without that test:
> [root@www2 opt]# time cfagent -K
> 
> real    0m16.229s
> user    0m0.320s
> sys     0m0.170s
> 
> 
> So the difference ist still quite big. You are probably right regarding the
> security checks, but those are not really necessary in this scenario
> where we just mirror in a HA environment, I think. So RSync seems to be
> doing just the right things here...
> 
> All tests have been run several times with differences <=10 sec. Encryption 
> does not seem to make a difference for cfagent. 
> 
> One thing is, that a "ps aux" shows a very different behaviour on the server:
> while rsync takes about 50% of cpu power on the server, cfservd stays under 2%
> 
> For me this seems to be the reason for the big difference. Did I miss any 
> configuration option?
> 
> 
> Regards, Daniel
> 
> On Fri, Jul 05, 2002 at 05:30:59PM +0200, Mark.Burgess@iu.hio.no wrote:
>> 
>> In a paper (not written by me) in 2001, with the older (slower)
>> protocol, it was shown that cfengine was *faster* tham rsync
>> at distributing files first time around. Rsync is faster at
>> updating certain kinds of changes (that the algorithm was designed
>> for -- small changes to large files). If cfengine is slower
>> at certain things it is because it is doing extra checking
>> for security reasons, but that applies to secure copy. This
>> is also much faster since version 2, so I do not know of any
>> real studies on this.
>> 
>> In short, I just do not believe the asssertion that cfengine
>> is slow at copying  large amounts of filespace, compared
>> to rsync. It doesn't tally with experiments done. Is this
>> just an assumption, or have you actually tried to measure
>> it and compare?
>> 
>> I am not keen on the idea of including librsync in cfengine.
>> It would not be a straightforward task, and cfengine is much
>> more security conscious than rsync. Sometimes there is a reason
>> to take your time and check stuff.
>> 
>> M
>> 
>> 
>> On  5 Jul, Adrian Phillips wrote:
>> >>>>>> "Daniel" == Daniel Riek <riek@de.alcove.com> writes:
>> > 
>> >     Daniel> Hi, we are using Cfengine in a environment where we need
>> >     Daniel> to copy large amounts of data from one machine to
>> >     Daniel> another. There are mainly to scenarios: software
>> >     Daniel> distribution (rpm packages and tarballs) and mirroring for
>> >     Daniel> a failover cluster.
>> > 
>> > Large as in ? I use copy for the whole cfengine "setup" from one
>> > machine to a backup, approximately 1GB which takes some minutes. I can
>> > understand anyone trying to anything more than this having problems.
>> > 
>> >     Daniel> One way would be to use RSync. That is what we would do in
>> >     Daniel> this environment if we had no Cfengine. But as we have
>> >     Daniel> some security issues and rsync would require at least a
>> >     Daniel> minimal root acces from the mirroring machine, we would
>> >     Daniel> prefere to use Cfengine.
>> > 
>> >     Daniel> Another reason for using Cfengine to copy the data is the
>> >     Daniel> possibility to have services restarted depending on the
>> >     Daniel> copy...
>> > 
>> >     Daniel> Unfortunately Cfengine seems to be very slow when doing
>> >     Daniel> such things.  This raises the question if anyone else
>> >     Daniel> tried to use Cfengine in this manner and what his
>> >     Daniel> experience is like?
>> > 
>> > One thing I'l like to do if possible was link in librsync and have
>> > some additional option to copy to make it use it instead. How much
>> > work this is and how much it will help I have no idea.
>> > 
>> > Sincerely,
>> > 
>> > Adrian Phillips
>> > 
>> 
>> 
>> 
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Work: +47 22453272            Email:  Mark.Burgess@iu.hio.no
>> Fax : +47 22453205            WWW  :  http://www.iu.hio.no/~mark
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> 
>> 
>> 
>> _______________________________________________
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>> Help-cfengine@gnu.org
>> http://mail.gnu.org/mailman/listinfo/help-cfengine
>> 
> 



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Work: +47 22453272            Email:  Mark.Burgess@iu.hio.no
Fax : +47 22453205            WWW  :  http://www.iu.hio.no/~mark
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~