Path: utzoo!mnetor!uunet!husc6!think!ames!ucbcad!ucbvax!jade!eris!mwm
From: mwm@eris.BERKELEY.EDU (Mike (My watch has windows) Meyer)
Newsgroups: comp.os.misc
Subject: Re: OS features
Message-ID: <6315@jade.BERKELEY.EDU>
Date: 16 Dec 87 22:13:00 GMT
References: <561@amethyst.ma.arizona.edu> <3228@tut.cis.ohio-state.edu>
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Reply-To: mwm@eris.BERKELEY.EDU (Mike (My watch has windows) Meyer)
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Mark Woodruff writes:
> o  Contiguous file allocation on large devices.  The additional overhead
>    of discontiguous file allocation is unwarranted on modern hardware.

Unicos (Cray's System V for their hardware) has transparent support of
files with large contiguous chunks, and an IO system that takes
advantage of them.

Each unix file system is broken up into two or more partitions (these
aren't unix partitions, but are more like the BSD cylinder groups).
The first partition is dedicated to special files, most notably
directories. Blocks for a data file are allocated contiguously as long
as no one else needs blocks in the partition. File creation
round-robins through all but the first partition of the file system,
to give the processes writing each file as much time as possible to
grow the file.

Unicos also supports disk striping. The results work fairly well, but
I don't know how much is do to which activity.