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From: terry@cs.weber.edu (A Wizard of Earth C)
Subject: Re: Dumb Question: Why 512 byte block?
Message-ID: <1992Dec20.025733.155@fcom.cc.utah.edu>
Sender: news@fcom.cc.utah.edu
Organization: University of Utah Computer Center
References: <1992Dec18.005050.20594@decuac.dec.com> <CGD.92Dec19000739@eden.CS.Berkeley.EDU>
Date: Sun, 20 Dec 92 02:57:33 GMT
Lines: 49
In article <CGD.92Dec19000739@eden.CS.Berkeley.EDU>, cgd@eden.CS.Berkeley.EDU (Chris G. Demetriou) 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. 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?
|>
|> sorry. you guys *both* sound confused. first of all, i've never
|> seen a FFS with 1k blocks; the most "standard" configuration
|> is 4k or 8k blocks, with 8 fragments.
|>
|> this yields fragments of (obviously) 512bytes and 1k.
|>
|> you can't split *fragments* between one file.
|> you *can* split blocks between one file, but this tends not to happen,
|> because the FFS doesn't do this unless it's necessary.
I totally mixed up blocks and fragments ...duh! The original posting was
talking about the "-k" option of the "df" command, and that's why I was
thinking of blocks (ie: "512-blks").
While I was looking at the du output:
hecate 1 % df
Filesystem 512-blks used avail capacity Mounted on
/dev/wd0a 591200 437684 94396 82% /
icarus:/home 1192464 1133390 35226 97% /icarus
einstein.att:/dsk2 2547712 1887656 410872 82% /X11R4
hecate 2 %
I should have thought about the fsck, which reports _fragmentation_ of the
file system.
I had been working for some time on a SVR4 UFS implementation, and I fear my
wheels were still jarred loose at the time I posted. ;-).
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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