*BSD News Article 9143


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From: wjin@cs.uh.edu (W. Woody Jin)
Newsgroups: comp.unix.bsd
Subject: Re: Dumb Question: Why 512 byte block?
Date: 19 Dec 1992 20:04:32 GMT
Organization: University of Houston
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Message-ID: <1gvv8gINN80e@menudo.uh.edu>
References: <1992Dec18.030833.7395@fcom.cc.utah.edu> <1gt736INNjje@menudo.uh.edu> <1992Dec18.235623.27538@fcom.cc.utah.edu>
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In article <1992Dec18.235623.27538@fcom.cc.utah.edu> terry@cs.weber.edu (A Wizard of Earth C) writes:
>
>You can't split blocks between files.  

Yes, you can.
For example, you may have 4K size block with 512 byte fragment size.

>A block is, by definition, the
>smallest possible allocation unit.  Thin about the case where you have
>a 1 byte file and a 1 block - 1 byte file; what would you do when
>adding one or two characters to the first (1 Byte)?  TReallocate?  Shift
>and reallocate for the last byte of the second file?
>
>But... you're right that it doesn't work the way I've shown... thought
>for sure I'd get bombarded on this one:
>
>Consider the most ridiculous possible situation:  I have a 1G disk with
>a 1G blocking factor (impossible without rewriting the buffering code).
>
>How many files can I have on the disk? (Ignore the blocks allocated to inodes
>and directoryies 8-P).
>
>The answer is "1"... even if it only has 1 byte in it.

In this case, if you have 512 byte fragment size, you use only one
fragment which is 512 byte.  And you must have 1G of buffer memory.

BTW, could anyone clarify whether 386BSD uses the Fast Unix File System
which is described in "A Fast File System For Unix" by McKusick, Joy, Leffler,
and Fabry (1984 ACM Tran. on Computer System) ?

-- 
____   ____  ____ ____________________________________ (___) _________________
|  |   |  |  |  |  W. Woody Jin (wjin@cs.uh.edu)       (o o)      Moo.... 
|  |   |  |__|  |  PhD Student. Research Asst.  o=======\ /  I'm  a Cow Lover.
|  |   |        |  Dept. of Computer Science   / |     ||O   My wife  was born
\  |---|  |--|  |  University of Houston      `  ||'---||    in Cow year. Mooo
 \____/|__|  |__| _______________________________^^    ^^_____________________