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Xref: sserve comp.periphs.scsi:19421 comp.os.386bsd.questions:9761 Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!msuinfo!agate!howland.reston.ans.net!EU.net!sunic!news.chalmers.se!not-for-mail From: tl@haddock.cd.chalmers.se (Torbj|rn Lindgren) Newsgroups: comp.periphs.scsi,comp.os.386bsd.questions Subject: Re: 6% UNIX overhead on SCSI disk? Date: 15 Apr 1994 23:20:12 +0200 Organization: Chalmers Computer Society Lines: 28 Message-ID: <2on0ec$14i@haddock.cd.chalmers.se> References: <FEN.94Apr13121431@imagine.comedia.com> NNTP-Posting-Host: haddock.cd.chalmers.se In article <FEN.94Apr13121431@imagine.comedia.com>, Fen Labalme <fen@imagine.comedia.com> wrote: >I've just installed the Maxtor, disklabled it, newfs'd and mounted it. >Yea! But when I did a `df` I saw that I was missing 6.1% of the disk! Assuming a standard BSD FFS - file system there is some amount of space that is reserved (BSD 4.3 used 10%). This space is only usable by root. It is possibel to change the percentage on the fly using tunefs, but it isn't advisable to set it too low (performance may suffer, but it shouldn't be any problems with 5% instead). Another thing that uses space is the inodes. By default there is one inode per 2048 byte, which means that the inodes take 10% of the space. For most partitions this is MUCH more than is needed (the main exception is usenet news partitions and /). I often use one inode per 4096 byte (5%), and most inodes are still unused (only one partition use more than 21% of the inodes using this setting). If you look at the output from df you can find the space after the inodes are allocated by looking at the "kbytes" field. If you add "used" and "avail" you get the free space after the reserved space is substracted. On most system you can get the defaults for this can be found in the man-page for newfs. For the NetBSD system I have access to the default is 10% and 1 inode per 2048 byte (also 10%), which means that approximately 20% of the space is unusable (at least almost). Most of the time I use 5% and 1 inode per 4096 byte (10% total).