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> This hardly seems like a win to have to pass over files twice, first to > see if they and up taking up more space than the OS reports, and a > second time to "compact" the strings of zeros. You might as well just > use a compression filter (gzip, bzip2), which can handle not only > strings of zeros, but anything else that repeats, and tokenize it on > the > fly in a single pass. > > This suggests that the --sparse option is effectively obsolete, given > the modern practice of almost always compressing tar archives. Exactly what I was just about to say ... after reading that man page. In short: . Never use --sparse when creating an archive that is compressed. It's pointless, and doubles the time to create archive. . Yes, use --sparse during extraction, if the contents contain a lot of serial 0's and you want the files restored to a sparse state. Thanks for looking up that detail. That explains why I had such poor performance with tar on windows - not because it was windows or cygwin, but because I was using --sparse and gzip during archive creation. > I'd say tar doesn't bring anything useful to this problem, given the > above info. If you only have one sparse file, you can get the same > benefit by simply doing: > > gzip -c --rsyncable sparse_file > desparsed_filed One error in your thinking: The man page saying "using '--sparse' is not needed on extraction" is misleading. It's technically true - you don't need it - but it's misleading - yes you need it if you want the files to be extracted sparsely. This, I believe, is the value-add that tar brings to sparsefile backup and restore, compared to straightup gzip.