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From: alan@shodha.enet.dec.com ( Alan's Home for Wayward Notes File.)
Newsgroups: comp.unix.ultrix
Subject: Re: Adding/setting up mem, disk, cd drive, sys admin?
Summary: Long Reply: Part Last.  How Full is Full?
	 or: "Say Goodnight Gracie..."
Message-ID: <3389@shodha.enet.dec.com>
Date: 16 Jun 91 06:47:44 GMT
References: <44675@netnews.upenn.edu>
Organization: Digital Equipment Corp. - Colorado Springs, CO.
Lines: 47



In article <44675@netnews.upenn.edu>, lau@desci.wharton.upenn.edu (Yan K. Lau) writes:
> I added 2 RZ57s in an expansion unit to the system.  I ran MAKEDEV and
> newfs.  The results were about 950megs total with 850megs available.  Is
> this normal?  I read somewhere that the system takes about 10% for
> (mumble...mumble).  

	And I responded "This seems to be normal".  But just to be
	sure I tried an experiment.  We also have a new expansion
	box with two RZ57s in it with which I've been able to experi
	ment.  The df(1) output for a new file system looks like:

	Filesystem         Total    kbytes   kbytes   %     
	node               kbytes   used     free     used  Mounted on
	/dev/rz1c          945726        9   851145     0%  /mnt

	Clearly the amount free and the amount used don't add up
	to the total.  If we take 10% off the total first though:

		945,726 - 94,572 = 851,154 = 851,145 + 9

	So it does work out.  What happens as the file system fills?
	I don't have the intermediate steps handy, but I do have the
	end result:

	Filesystem         Total    kbytes   kbytes   %     
	node               kbytes   used     free     used  Mounted on
	/dev/rz1c          945726   945726        0   111%  /mnt

	The "kbytes free" went to 0 the same time the %used went to
	100%.  After that "free" continued to be zero as I slowly
	filled up the rest of the disk.  So a completely full file
	system will end up at 111% full, which makes sense when you
	think about it.

	Finally; getting that last few blocks used up wasn't easy.
	I create a bunch of large files initially by making copies
	of /dev/mem into the file system.  When I got enough of those
	I made a another that took up most of the rest and slowly
	appended stuff onto the end of it until I got file system
	full messages.  At this point I had just a few KB left over.
	These last few I picked up by creating an appropriate number
	of small files of 1 KB each.  I still had lots of inodes left 
	though.
-- 
Alan Rollow				alan@nabeth.cxn.dec.com