I think rsync will compare the timestamp and size first, if they are the same, rsync will skip, is that right? If so, it would be faster I think.<br><br><div class="gmail_quote">2009/8/11 Michal Suchanek <span dir="ltr"><<a href="mailto:hramrach@centrum.cz" target="_blank">hramrach@centrum.cz</a>></span><br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
2009/8/11 Ming Gao <<a href="mailto:gaomingcn@gmail.com" target="_blank">gaomingcn@gmail.com</a>>:<br>
<div>> It's almost the same? I ever tested on about 7G data, I rsync'ed it to<br>
> another directory, and it takes less than 1 minute when I run the same<br>
> command line again.<br>
<br>
</div>Did you test it on the two NFS shares or something else?<br>
<br>
Also if you have enough memory part of the data might remain cached<br>
and speed up subsequent transfers.<br>
<div><br>
><br>
> The reason why I use rsync is that the data will change during the time I<br>
> run rsync the first time. Then I need to run rsync the second time to make<br>
> them the same.<br>
><br>
> How long would it take if the two copies are the same? I mean just verify if<br>
> they are the same.<br>
><br>
<br>
</div>If both source and destination are NFS mounted and they are on<br>
reasonably fast drive array then the bottleneck is the network.<br>
<br>
Reading src & dest and comparing them is about as fast as reading src<br>
and writing dest because the whole data gets through the network twice<br>
in either case. The latter is probably faster because the system<br>
simply moves frames between ethernet card buffers without doing much<br>
else, comparing may get quite CPU intensive and slow the process down.<br>
<br>
The advantage of rsync comes when you have disks attached directly and<br>
the network link is slow - the checksums can be computed locally and<br>
only the differences transferred.<br>
<br>
You would have to run rsync on the two NFS servers for it to help, and<br>
it only helps if the disk speed (and computation speed) is<br>
substantially faster than the network transfer speed.<br>
<br>
HTH<br>
<font color="#888888"><br>
Michal<br>
</font></blockquote></div><br>