Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!uxc.cso.uiuc.edu!garcon!mrcnext.cso.uiuc.edu!carlson
From: carlson@mrcnext.cso.uiuc.edu
Newsgroups: comp.sys.next
Subject: Re: OD
Message-ID: <800008@mrcnext.cso.uiuc.edu>
Date: 21 Jun 89 20:11:00 GMT
References: <3985@tank.uchicago.edu>
Lines: 37
Nf-ID: #R:tank.uchicago.edu:3985:mrcnext.cso.uiuc.edu:800008:000:1421
Nf-From: mrcnext.cso.uiuc.edu!carlson    Jun 21 15:11:00 1989


Part of the disk space is used for i-nodes (control info).
Also, 10% is reserved, for efficiency and for emergencies.
(No specific area of the disk is set aside,
the system just keeps at least 10% free at all times.)
The 236MB is what's left for general users, and this is the 100% usage
figure from df(1).  Only the superuser can use reserved space,
and could run usage up to 110%.

The sector size is (usually) 1k.
A storage block is 8k, with 1k fragments. 
See fs(5), fstab(5), and /etc/fstab.

Example:
#	@(#)disktab	4.11 (Berkeley) 5/31/86
# Disk geometry and partition layout tables. 
# Key:
#	ss	sector size -- MUST ALWAYS BE DEV_BSIZE (1024) FOR NOW
#	b[a-h]	partition block sizes in bytes
#	f[a-h]	partition fragment sizes in bytes
#	d[a-h]	partition density (bytes-per-inode)
#	r[a-h]	partition minfree
#
# [da -> 1 inode per 8k disk data space (quite generous, actually)]
# [..... with a full disk, we only use 17% of inodes]
# [ra -> reserve 10% disk space]
omd-1|OMD-1|Canon OMD-1:\
	:ty=removable_rw_optical:nc#1029:nt#15:ns#16:ss#1024:rm#3000:\
	:fp#256:bp#256:ng#153:gs#1600:ga#16:ao#784:\
	:os=odmach:z0#80:z1#168:ro=a:\
	:pa#0:sa#242352:ba#8192:fa#1024:ca#6:da#8192:ra#10:oa=time:\
		:ia:ta=4.3BSD:aa:
#
# One model of the 330M disk used 512 byte sectors.
--------------------
Brad Carlson  <carlson@mrcnext.cso.uiuc.edu> or <b-carlson@uiuc.edu>
University of Illinos--Micro Resource Center--NeXT guru