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The kernel.org repository depends heavily on compression to keep its storage and bandwidth expenses down. An uncompressed tarball for the 2.6.32 release weighs in at 365MB; if downloaders grabbed the data in this format, the resulting bandwidth usage would be huge. So kernel.org does not make uncompressed tarballs available; instead, one can choose between versions compressed with gzip (79MB) or bzip2 (62MB). Bzip2 is the newer choice; it took a while to catch on because the needed tools were not widely shipped. Now, though, the folks at kernel.org are considering making a change in the compression formats used there.
What's driving this discussion is the availability of the XZ tool, which is based on the LZMA compression algorithm. XZ offers better compression performance - 53MB on that 2.6.32 tarball - but it suffers from a familiar problem: the tools are not yet widely available in distributions, especially those of the "enterprise" variety. This has led to pushback against the idea of standardizing on XZ in the near future, as can be seen in this comment from Ted Ts'o:
In fact, there is little pressure to replace the gzip format anytime in the near future. Its compression performance may not be the best, but it does have the advantage of being far faster than any of the alternatives. From the discussion, it is fairly clear that some users care about decompression time. What is more likely is that XZ might eventually displace files in the bzip2 format. Then there would be a clear choice: speed and widespread availability or the best available compression. Even that change, though, is likely to be at least a year away; in the mean time, kernel.org will probably carry files in all three formats.
(This discussion also included a side thread on changing the 2.6.xx numbering scheme. Once again, though, the expected flame wars failed to materialize. There just does not seem to be much interest in or energy for this particular change.)
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