From: jmd@cube.handheld.com (Jim De Arras)
Subject: Re: 1024 byte sector errors with newfs??
Organization: Hand Held Products, Inc.
Date: Tue, 6 Oct 1992 02:03:38 GMT

In article <1992Oct4.061642.12564@csus.edu> eps@futon.SFSU.EDU (Eric P. Scott)  
writes:
> In article <1992Oct1.020322.1754@cube.handheld.com>
> 	jmd@cube.handheld.com (Jim De Arras) writes:
> >                                   Well, the problem (if it is one) is that
> >newfs (and BuildDisk) make a table for the fs that generates a warning that  
the
> >4096 bytes per inode is not possible, and it will use 4490 bytes per inode.
> >Not knowing enough about the topic, I just 'feel' that the 4490 bytes per  
inode
> >will be a bad fit on a 1024 bytes per sector HD.
> 
> bytes per inode has nothing to do with sector size.  It's a guess
> of the average file size on that filesystem.
> 
> Each filesystem has space for file data, and space for inodes.
> You need one inode for each file.  If you run out of inodes,
> you can't create any new files.  If you have more inodes than
> you need, you have less space available for file data.  You can
> choose where to draw the line, but it's obviously safer to err on
> the side of more inodes.
> 
> How many inodes do you need?  That depends on how many files you
> want to have.  For most people, that's directly related to
> filesystem size.  If you have bigger disks, you can have bigger
> filesystems, and if you have bigger filesystems, you can store
> more files.  Assuming that things scale linearly, the average
> file size remains more or less constant.  So rather than
> specifying the number of inodes, you're adjusting the inode-to-
> data ratio.  If, for example, you're setting up a filesystem to
> spool usenet news, you're going to want to tune it for primarily
> a lot of small files (RTF silliness notwithstanding).  If you're
> going to have a huge swapfile in there, you can reduce the number
> of inodes, etc.
> 
> Things are complicated somewhat by cylinder group constraints.
> In particular, each cylinder group can only hold 2048 inodes.
> The warning you saw meant that you didn't have enough cylinder
> groups to supply the number of inodes you requested.  By reducing
> the cylinders/cylinder group ratio, you got more cylinder groups.
> Optimum values are a function of disk geometry, and thus vary
> between drive models.
> 
> If none of this makes any sense to you, check out chapter 7 of
> _The Design and Implementation of the 4.3BSD UNIX Operating
> System_ by Leffler, McKusick, Karels, and Quarterman, which has a
> reasonably detailed explanation of the Berkeley FFS.
> 
> 					-=EPS=-

Thank you, that does help me understand it better.  I will get that book, too.   
A specific question, though.  I am not up to hand building a complete NeXT  
release disk.  How can I convince BuildDisk to use different parameters?  I can  
change newfs parameters to change the defaults, but BuildDisk wants to do it  
all over.

I ask in the group as I've received a number of e-mail messages asking me to  
relay any information I get.  There is some confusion in this area, and some  
folks that want to reformat to 1024 byte sectors are concerned.

Jim