Date: Thu, 01 Mar 2007 17:34:02 -0500 From: Lowell Gilbert <freebsd-questions-local@be-well.ilk.org> To: Ivan Voras <ivoras@fer.hr> Cc: freebsd-questions@freebsd.org Subject: Re: defrag Message-ID: <44r6s8y4o5.fsf@be-well.ilk.org> In-Reply-To: <es7im6$9tu$1@sea.gmane.org> (Ivan Voras's message of "Thu\, 01 Mar 2007 23\:04\:52 %2B0100") References: <539c60b90703010849x33dd4bbbt8f6ca6aa0c8e83a0@mail.gmail.com> <es7gv6$3is$1@sea.gmane.org> <20070301165055.638b0a06.wmoran@collaborativefusion.com> <es7im6$9tu$1@sea.gmane.org>
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Ivan Voras <ivoras@fer.hr> writes: > Bill Moran wrote: >> In response to Ivan Voras <ivoras@fer.hr>: > >>> 352462 files, 2525857 used, 875044 free (115156 frags, 94986 blocks, >>> 3.4% fragmentation) > >> >> Just to reiterate: >> "Fragmentation" on a Windows filesystem is _not_ the same as "fragmentation" >> on a unix file system. They are not comparable numbers, and do not mean >> the same thing. The only way to avoid fragmentation on a unix file system >> is to make every file you create equal to a multiple of the block size. > > Ok, my point was that 3.4% is a low number for a long used system, but, > for education sake, what is the difference between Windows' > "fragmentation" and Unix's "fragmentation"? > > I believe that a "fragmented file" in common usage refers to a file > which is not stored continuously on the drive - i.e. it occupies more > than one continuous region. How is UFS fragmentation different than > fragmentation on other kinds of file systems? > > UFS has cylinder groups, blocks and block fragments. Obviously, a file > larger than a cylinder group will get fragmented to spill over to > another cylinder group. Block fragments only occur at the end of files. If you know the standard computer science terminology, it can be described quite tersely. UFS fragmentation is a way of avoiding internal fragmentation from wasting too much space. MS-DOS-FS fragmentation is an example of external fragmentation in the storage space. They don't really have anything to do with each other. -- Lowell Gilbert, embedded/networking software engineer, Boston area http://be-well.ilk.org/~lowell/
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