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Simon Williams wrote: > I'm in the process of reorganising my backup system, and was wondering > if anyone had any thoughts on how effective rsync's -z (compression) > option is on fast links (100Mbps ethernet). > > There must come a point when compressing the data takes longer than it > would to just send it over the link as is- the question is what ratio of > processor speed to link speed would this happen at? > Minimum processor speed is 1Ghz for the machines concerned. Backuppc (A great tool for backups that manages all this for you) - uses rsync and compression and recommends a setting around 2 (0-9) but of course it's entirely dependant on the two machines, their loads, free memory as well as disk space and of course bandwidth. Certainly increasing the compression ratio expands CPU usage exponentially and you start to see a reduction in effectiveness. Also worth factoring is whether a human will be using either machine during the backup and if so, will a CPU hungry app become a nuisance to them? Because of the above I'm only using 2 having dabbled with 3 or 4 and found them causing major system lag both on server and client on machines in excess of 1Ghz. Even now I'm not totally happy and may drop to 1; disk space is cheap and bandwidth is less important on my 100mbit lan than cpu usage is. So... Suck it and see, tweak and tune until you've got it right for your system. -- Simon Avery -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html