200gb hard drive?

Jerry McAllister jerrymc at clunix.cl.msu.edu
Thu Nov 20 13:18:02 PST 2003

> Omer, this is because a percentage of your disk space is reserved
> automatically by FreeBSD. I believe that it automatically reserves 8% of
> your disk space. You can adjust this by using 'tunefs'. Try 'man tunefs' to
> find out how to use tunefs.

Partly true for the second part of the question - eg why it says
there is 183G but 169G is reported as 0% free.

But, the first part is because manufactures advertise their disk
sizes in decimal where a GBYTE - 1,000,000,000 bytes, but the
system uses more common convention where the most convenient
binary equivalent is used to report sizes.
In this, 1 KByte = 1024 bytes, 1 MByte = 1,048,576 bytes
and 1 GByte = 1,073,741,824 bytes.

So, the manufacturers advertising is only 93.1323 % of what you think
you will be getting according to the way the system reports it.
For 200 GBytes, that amounts to 186.26 GBytes.   That gets a little
further reduced bye "formatting" (fdisk, disklabel, newfs work) leaving
about 183 GBytes of disk if reported according to the more common
binary equivalent method.

Then the system reserves some for various real and historical reasons
when it interprets how much a non-root account can write to disk.
I think the other responder is correct that the default is 8.0 %.
So, take out 8 % from 183 GBytes and you get about 169 GBytes.

It is all there if you know the system and the arithmetic.

The biggest confusion comes in the manufacturers reporting
in decimal because it makes the disks they are selling sound
bigger.   Of course, there are some who swear that is the correct
way to define disk size.  But, I think that since the normal usage
is by nearest binary equivalent K-s, M-s and G-s, it is somewhat
disengenuous for manufacturers to insist on doing it by decimal.

This has been discussed so many times in the Email list, that if
one does a little searching, it should be impossible to avoid
finding this type of information.   So, do a little searching.
In this case Google and pretty much any search engine out there
can be your friends.


> David van Geyn
> ----- Original Message -----
> From: "Omer Faruk Sen" <freebsd at faruk.net>
> To: <freebsd-questions at freebsd.org>
> Sent: Thursday, November 20, 2003 3:23 PM
> Subject: 200gb hard drive?
> > Hi
> >
> > I have installed a new hard drive to my FreeBSD system. Hard drive is
> 200gb
> > but
> > when I fdisk and disklabel the output of "df -h" is something like that:
> >
> > /dev/ad1s1e   183G   2.0K   169G     0%    /disk2
> >
> > Here as you can see I can only use 169GB of it. Bios has seen my harddrive
> > as 190GB also dmesg output is like that:
> >
> > ad1: 190782MB <WDC WD2000JB-00DUA3> [387621/16/63] at ata0-slave UDMA100
> >
> > My question is what happened to 190-169 gb or maybe after some filesystem
> > information reservation what happened to 183-169 gb?
> >
> > By the way I have used default newfs parameters -b 16384 -f 2048. I don't
> > know if that helps...
> >
> > REGARDS...
> >

More information about the freebsd-questions mailing list