A checksum question

jw schultz jw at pegasys.ws
Wed Mar 26 05:13:54 EST 2003

On Tue, Mar 25, 2003 at 04:31:00PM +0000, Terry Raggett wrote:
> I'd like to know a little about the internals of RSYNC. I am a little 
> confused as to why RSYNC is using both the simple 32 bit algorithm and 
> the MD4 checksum function on the same files. From my testing this causes 
> a vast overhead that is clearly not represented by RCP (fairly 
> obvious!). Removing checksumming from a secure whole-file LAN transfer 
> brings RSYNC in line with the general performance of RCP.
> Can someone explain to me the rationale behind the checksum algoritm and 
> use within the RSYNC protocol?
> I'm asking this question as I am finding it rather difficult to convince 
> some of our users that RSYNC is a viable replacement for RCP 
> functionality, which is necessary to resolve some of the limitations we 
> encounter with the standard RCP.
> Many thanks in anticipation,
> Terry Raggett

Rsync is not a replacement for rcp.  Rcp is a remote-copy
utility.  Rsync is a remote-update utility.  They each exist
for completely different purposes.

Without knowing what limitations you are encountering with
rcp or to the specific purpose of use i couldn't speak to
the suitability of rsync.  There are many times that rsync
is not the best or most efficient tool for the job.  If all
you want is a fast light-weight copy utility, rsync isn't
it.  There are even times when rsync is ill suited to an
update operation.  The tool-box was invented for a reason.

	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt

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