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From: terry@cs.weber.edu (A Wizard of Earth C)
Subject: Re: Dumb Question: Why 512 byte block?
Message-ID: <1992Dec20.031324.436@fcom.cc.utah.edu>
Sender: news@fcom.cc.utah.edu
Organization: University of Utah Computer Center
References: <1992Dec18.030833.7395@fcom.cc.utah.edu> <1gt736INNjje@menudo.uh.edu> <1992Dec18.235623.27538@fcom.cc.utah.edu> <1gvv8gINN80e@menudo.uh.edu>
Date: Sun, 20 Dec 92 03:13:24 GMT
Lines: 44
In article <1gvv8gINN80e@menudo.uh.edu>, wjin@cs.uh.edu (W. Woody Jin) writes:
|> 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.
Mixed up blocks and frags in the context of the original post (re: the "df"
command). You are, of course, right.
|> 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) ?
Yes, it does.
....
My point was that disk allocation was quantized at larger than 1 byte
increments, and the larger those increments, the more space is actually
used by a 1 byte file. My examples were correct for 4k blocks with 8
frags per block.
The summation of this being that upping the size of a block will up the
size of the _fragments_ of that block unless the number of fragments per
block is also increased (isn't 8 the limit?). The problem here being,
the disk will disappear faster with 8k/8 block frags than it will with
4k/8 blocks frags because of the number of files whose lengths aren't on
block boundries.
A smaller absolute fragment size (however it is arrived at) will result in
less absolute disk real estate being take up for odd-sized files.
Terry Lambert
terry@icarus.weber.edu
terry_lambert@novell.com
---
Any opinions in this posting are my own and not those of my present
or previous employers.
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