On Tue, 2006-Aug-01 23:35:03 -0700, Tim Kientzle wrote: >The "cheap" solution is to handle it purely on >extract: Detect blocks of zeros when restoring >files and seek over them.
The downside is that you wind up with a sparse file whether or not you wanted one. > I simply dislike >the GNU tar approach, in part because it requires >two passes over the file (the map of holes is required >before the file is written). Actually, the only real solution to copying sparse files is to add a system call that can return a map of holes. This would neatly address the "needs two passes" problem with tar. As a general comment (not addressed to Tim): There _is_ a downside to sparsifying files. If you take a sparse file and start filling in the holes, the net result will be very badly fragmented and hence have very poor sequential I/O performance. If you're never going to update a file then making it sparse makes sense, if you will be updating it, you will get better performance by making it non-sparse. -- Peter Jeremy
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