Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!oliveb!jerry From: jerry@oliveb.olivetti.com (Jerry Aguirre) Newsgroups: comp.unix.wizards Subject: Re: A few questions about 4.3BSD partitions and cylinders Message-ID: <13380@oliveb.olivetti.com> Date: 21 Jan 88 07:28:34 GMT References: <11271@brl-adm.ARPA> Reply-To: jerry@oliveb.UUCP (Jerry Aguirre) Organization: Olivetti ATC; Cupertino, Ca Lines: 37 In article <11271@brl-adm.ARPA> rbj@icst-cmr.arpa (Root Boy Jim) writes: > > From: Doug Alan > > This leads me to ask some more questions that have been bugging me for > a while. Why is the root partition always 15884 sectors? Where does > this number come from? Can you make it bigger or smaller? Will this > cause any problems? Why is swap space usually 33440 sectors? Why is > >For hysterical raisins. I think they come from the gee I'm a tree of >the RP06. It just seemed convenient for all root file systems to be >the same size, so they can be dd'ed easily. Except they arn't. Even though the disktab may specify the same 15884 size, newfs/mkfs is going to create different sizes for different disks. Because the number of sectors in a cylinder are different the number of inodes changes and that also changes the number of free sectors. Also the 15884 results in the last cylinder being a partial one so some of the sectors are "cannot be allocated". (I spent hours explaining to one of our guys why an eagle-II had a different size root from an eagle-I even though they had the same 15884 entry.) Of course if you dd then it doesn't matter bacause you won't be paying any attention to cylinder boundries. Given the level of access to root files (/bin /etc /lib) this could negate much of the benifits of the cylinder group concept. I presume that the only reason that anyone would dd a root file system would be if they were bootstrapping another system. If they were going to get that far into it they could patch the destination file system while they booted. Meanwhile I waste over half a meg of my root file system as either hidden or unusable. I could use that space to hold all those timezone files in /etc/zoneinfo. Jerry Aguirre Systems Administration Olivetti ATC