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