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Re: announce: readahead-1.4

At 5:38 PM -0600 3/7/07, Callum Lerwick wrote:
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>On Wed, 2007-03-07 at 12:55 -0500, Tony Nelson wrote:
>> Microsoft already addressed that issue in WinXP, which has fancy hooks to
>> the disk defragmenter so that there isn't much seeking when booting WinXP
>> (it does take several days until the defrag happens).  So I agree with
>> Callum, and also dunno WTR MS is thinking.
>> Probably readahead adopting what MS did in WinXP would be most effective
>> but would also violate the most MS patents, as well as requiring hooking
>> into the filesystem rather more than is wanted.  Something like UnionFS
>> might work without patent issues, if it could use a file instead of a hard
>> partition.
>I don't see how they could patent defragging a disk. Lets not get crazy
>here. ext3 does a decent job of not fragmenting files unnecessarily, can
>we really gain much more than the current readahead solution?

You don't understand the brilliance of what they did.  They "refragment"
the disk so that all disk I/O during boot is sequential, no matter what
file is being read or what part of that file.  This Microsoft paper seems
relevent: _Fast System Startup for PCs Running Windows_.  Look at the
section "Prefetching":


AIUI, WinXP doesn't prefetch whole files, but only the parts that would
have been fetched anyway.

Note that reading this paper won't increase Fedora / Redhat patent
exposure, as it dosen't explicitly say which things are patented, though I
expect that all of them are, so using any of them would be risky even
without reading the paper.
TonyN.:'                       <mailto:tonynelson georgeanelson com>
      '                              <http://www.georgeanelson.com/>

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