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De-Danish this. Add a lot more chatty commentary in my own inimitable style.

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Jordan K. Hubbard 1994-11-05 06:54:49 +00:00
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@ -1,46 +1,66 @@
How to assign disk-space to FreeBSD.
How to assign disk space to FreeBSD.
1. What is all this about
--------------------------
After a general introduction, you will find explanations on what you need
to do to assign space for FreeBSD on your disk(s). The program documented
herein is the "sysinstall" program which lives on the install-disks.
1.1 What is the problem
------------------------
The problem is that disks are big. So big that people don't want to use them
in one piece. With the latest disks being in the 9.0 Gbyte range (which for
comparision is some six thousand floppydisks of the 1.4 Mb type) you cannot
blame them. It has always been this way, and most computers have some way
of "slicing" the disks into more manageble chunks.
1.2 A history-lesson
1.0 Getting started.
---------------------
MS-DOS, when hard-disk support was slammed on back in the late eighties,
didn't have this. What it had was a way to install Xenix and MS-DOS
on the same disk (MicroSoft were in the UNIX-business once, remember ?).
In the first sector on the disk, was a piece of "boot-code" and a table
with four entries. Each of those entries pointed at a slice of the disk,
and one of them was marked "active". The machine would boot by reading
the first sector into RAM, and jump to it. The small piece of boot-code
would look at the table and decide which OS was to be booted by looking
for the "active" flag, load the first sector of that slice of the disk
and jump to it.
Later of course, they realized that disks could be bigger than the 32Mb
the FAT-12 "filesystem" could handle, so they added a kludge: They had
two MSDOS slices, a "Primary" and a "Secondary". The primary could still
only be 32Mb, but the Secondary had no size limit. And the trick was, it
had another MBR in it, so now suddenly 5 slices could be availabel to
MS-DOS, later the made the Secondary MBR recursive, and thereby effectively
avoided any number limit. Of course you can still only have the 26 slices
in MSDOS because they use "drive-letters".
After a general introduction, you will find some explanation on what you need
to do to assign space to FreeBSD on your disk(s). This is done through
the "sysinstall" program, which lives on the inital boot floppy. Those
already expert with PCs may wish to skip ahead to section 1.2, the rest of
you may enjoy the brief history lesson.
1.3 What FreeBSD does
1.1 The ins and outs of allocating disk storage on your PC.
------------------------------------------------------------
Modern hard disk drives are now getting big enough that people don't want
to allocate all of one to just one operating system anymore, especially
given the increasing size of disk drives (the latest 9.0 Gbyte models holding
the equivalent of some six thousand 1.44MB floppies!) and the virtual
explosion of operating system options available for the PC. To solve this
problem, IBM came up with a scheme for "slicing" the disks into more manageble
chunks, or partitions. It works, but only just. To better understand
why, first a brief bit of history:
MS-DOS, when hard disk support was unceremoniously grafted on back in the
late eighties, didn't have such things. What it had was a way to install
Xenix and MS-DOS on the same disk (Remember when Microsoft were in the UNIX
business? A long time ago, to be sure!).
In the first sector on the disk was a piece of "primary boot code" and a table
with four entries. Each of those entries pointed at an arbitrary slice
of the disk, with one of them was marked "active". The machine would boot
by reading the first sector containing the boot code into RAM and then
jumping to it. The job of this small piece of boot code was to look at
the 4 entry table and decide which OS was to be booted by looking
for the "active" flag. It would go and load the first sector of that slice
of the disk into RAM and then and jump to it in turn. This bit of boot
code was called the "secondary boot", and could be specific to a given
operating system. The primary boot code and 4-entry table is known
as the Master Boot Record, or MBR, and is very important to the proper
operation of your PC! We will discuss the MBR in more detail later.
It was later realized, with the hindsight that IBM is famous for, that disks
could be bigger than the 32Mb that the early DOS FAT-12 file system could
handle, so they added a kludge: They had two MSDOS slices, a "Primary" and
a "Secondary". The primary could still only be 32Mb, but the Secondary had
no size limit. And the trick was that the secondary had ANOTHER "table entry"
so that now suddenly up to 5 slices could be available to MS-DOS. The
Secondary boot record was later made recursive, thus effectively avoiding
any fixed limit. Of course, they were still stuck with a maximum of 26 slices
given the use of "drive letters" in DOS. Yes, truly DOS was and is an
utterly terrible operating system, which of course explains its amazing degree
of success. Anyway, this all brings us up to today, which is where FreeBSD
comes in.
1.2 What FreeBSD does
----------------------
FreeBSD has, like any other UNIX, a concept of "partitions". There is no
difference between a slice and a partition as such, but we use the two
words to distinguish between the two different levels of slicing.
FreeBSD has, like any other UNIX-like operating system, the concept of
"partitions." Partitions are used to implement its own "slicing" abstraction,
and although there is no real difference between a slice and a partition as
such, we use the two words to distinguish between these two different levels
of slicing.
The result is that we have a two-tier structure on the disk:
@ -59,127 +79,172 @@ The result is that we have a two-tier structure on the disk:
+-------------------+ \ +----------------+
| Partition C | --> | swap-partition |
+-------------------+ +----------------+
...
| ... |
Here is the rule-set that FreeBSD uses:
Here are the rules that FreeBSD plays by:
A: FreeBSD always has a MBR-slice with type 0xa5. This means that there
should always be a MBR-record, even in the case where FreeBSD occupies
the entire disk.
B: The FreeBSD-slice contains the FreeBSD-disklabel in the second sector.
C: The 'C' partition in the FreeBSD-disklabel corresponds to the entire
FreeBSD-slice.
A: FreeBSD always has an MBR slice with type 0xa5 (each of the 4 slices can
also have a unique integer identifier so you can tell your DOS slices
from your FreeBSD slices from your Linux slices, etc). This means that
there should always be an MBR record, even in the case where FreeBSD
occupies the entire disk.
B: The FreeBSD slice contains the FreeBSD disklabel in the second sector
(remember, the first sector contains the secondard boot code for FreeBSD,
which is what prints that FreeBSD prompt at you when you first boot
FreeBSD from a floppy or hard disk).
C: The 'C' partition in the FreeBSD disklabel corresponds to the entire
FreeBSD slice.
D: The 'D' partition corresponds to the entire physical disk.
E: Should a disk not have a FreeBSD-slice (because there simply is no
FreeBSD on it anywhere), then the MBR-slices are mapped into partitions
'E' to 'H' of a artificially created FreeBSD-disklabel.
E: Should a disk not have a FreeBSD slice (because there simply is no
FreeBSD on it anywhere), then the MBR slices are mapped into partitions
'E' to 'H' of a artificially created FreeBSD disklabel. This is useful
for getting at DOS-only disks.
Therefore, to get FreeBSD onto your disk, you need to do the following:
1. Make a MBR-slice for FreeBSD (FDISK)
2. Partition the diskspace in the MBR-slice into partitions (DISKLABEL)
Step FreeBSD utility
------------------------------------------------------------ ---------------
1. Make an MBR slice for FreeBSD (FDISK)
2. Partition the diskspace in the MBR slice into partitions (DISKLABEL)
3. Assign mount-points to the partitions. (DISKLABEL)
2. The main-screen
-------------------
The main-screen shows you the current status, It shows you which disks
2. The sysinstall utility
--------------------------
The sysinstall utility is the program you first see when you boot
FreeBSD's install floppy. It is responsible for partitioning your
disk, creating an MBR slice for FreeBSD, setting up the disklabel
within that slice and creating filesystems for each FreeBSD partition
you create within that slice. It is composed of a number of screens.
These are described below.
2.1 The main screen
--------------------
The main screen shows you the current status, It shows you which disks
FreeBSD has found, how big they are and how much of it is assigned to
FreeBSD in a FreeBSD-MBR-slice. It also shows the partitions which have
had a mountpoint assigned to them.
FreeBSD in a FreeBSD MBR slice. It also shows the partitions which have
had a mountpoint assigned to them (not necessarily FreeBSD partitions;
FreeBSD is perfectly capable of mounting DOS disks directly).
(H)elp -- shows you this file.
(F)disk -- enters the Fdisk editor, where you can change the MBR-record.
This is what you want to use to assign some part of the disk to FreeBSD.
(F)disk -- enters the Fdisk editor, where you can change the MBR record.
This is what you want to use to assign some part of the disk to FreeBSD.
(D)isklabel -- enters the Disklabel editor, here you can change how the
FreeBSD slice is used.
FreeBSD slice is partitioned for FreeBSD.
(Q)uit -- will continue the installation process.
3. FDISK - how to make an MBR-slice
2.2 FDISK - how to make an MBR slice
-------------------------------------
There is some rules to follow everywhere, and the MBR is a potential mine-
field. There is no way to really make sure that you have a valid MBR. It
is very complicated to write a validation check for it, because there are
no real rules.
There are some rules to follow here since altering your MBR is a potential
minefield. There is really no way for the sysinstall program to genuinely
know that you have a valid MBR, so you have to be extra careful in what
you edit. Failure to do this properly can and will destroy your other
operating system entries!
Even if you don't plan to have MSDOS on this disk, make a MSDOS slice
Even if you don't plan to have MSDOS on a disk, make an MSDOS slice
using the MSDOS's FDISK.COM program. The reason for this is that if you
do it that way, you are 100% sure that FreeBSD will use the same number
of heads, sectors and cylinders as MSDOS would use. If you don't plan
to have MSDOS on the disk, just (D)elete the slice in the FreeBSD's
(F)disk editor.
of heads, sectors and cylinders as MSDOS would use. If you really don't plan
to have MSDOS on the disk, just (D)elete the slice in the FreeBSD's (F)disk
editor.
From the main-screen press 'F' to enter the MBR editor. You have five
From the main screen press 'F' to enter the MBR editor. You have five
commands available:
(H)elp -- Will launch you into this file.
(H)elp -- Shows you this file.
(D)elete -- Will delete a slice entirely.
(D)elete -- Deletes a slice entirely.
(E)dit -- Will allow you to edit a slice. It will ask how many megabytes
you want to assign to this slice, and will suggest the maximum possible
as default. It might say zero, even though there is disk-space available,
then you need to delete and recreate the other partitions to get the
puzzle solved. It will then ask you what type to give the slice, and
the default here is 0xa5, which is a FreeBSD slice. You can enter any
other number here too, which can be useful as a placeholder. Finally
it will ask you about the "boot-flag", 0x80 means "boot from this" and
anything else means "don't".
If you specified a FreeBSD slice, any existing slices witht the 0xa5
type will be reset to 0x00 "unused". FreeBSD only supports one slice
per disk for FreeBSD.
(E)dit -- Allows you to edit a slice. It will ask how many megabytes
you want to assign to the slice, and will suggest the maximum possible
as a default. It might say zero, even though there is disk space available,
in which case you will probably need to delete and recreate the other
partitions to get it to see where the free space is.
It will then ask you what type to give the slice, for which the default is
0xa5 (a FreeBSD slice). You can enter any other number here too, which can
be useful as a placeholder for some other OS you plan to install later.
Finally, it will ask you about the "boot flag". 0x80 means "boot from this"
slice by default, and anything else means "don't".
If you specified a FreeBSD slice, any existing slices with the 0xa5
type will be reset to 0x00 "unused". FreeBSD only supports one slice
per disk for FreeBSD.
(R)eread -- This is your "undo" function. It will read the data of the
disk again.
disk again, disposing of any changes you may have made.
(W)rite -- When you are satisfied with the data, this function will write
the new MBR to the disk.
the new MBR to the disk.
(Q)uit -- Go back to the main-screen.
(Q)uit -- Go back to the main screen.
4. Disklabel - How to divide the FreeBSD-slice.
------------------------------------------------
2.3 Disklabel - How to divide up the FreeBSD slice.
----------------------------------------------------
(H)elp -- Will launch you into this file.
The disklabel screen provides the following commands:
(S)ize -- Will resize a partition for you, it will suggest as default the
(H)elp -- Shows you this file.
(S)ize -- Resizes a partition for you, it will suggest as a default the
maximum amount of diskspace it can find. This algorithm isn't too smart
so it might say zero, even though there is diskspace available. If it
and may say zero, even though there is diskspace available. If it
does, delete and resize the other partitions.
(M)ountpoint -- Here you assign where the filesystem in a partition is to
be mounted. 'b' partitions will always be made into "swap" partitions.
be mounted. `b' partitions will always be made into "swap" partitions.
(D)elete -- Will delete a partition.
(D)elete -- Delete a partition.
(R)eread -- Is a undo function. It will reread the current disklabel from
(R)eread -- The undo function. It will reread the current disklabel from
the kernel.
(W)rite -- This will write the disklabel to the disk. You must always write
before you quit, otherwise your changes will be lost.
(Q)uit -- Exit back to the main-screen.
(Q)uit -- Exit back to the main screen.
5. Some hints on diskspace needed
----------------------------------
2.4. Hints on partition sizing
-------------------------------
5.1 Swapspace
--------------
Always assign at least as much diskspace to swap as you have RAM in the
machine. If you expect to run X11 (XFree86) on the machine, twice that
amount.
While it's impossible to say how much space you're going to want to
make your various partitions without knowing more about your intended
applicatins, here are some good rules of thumb to follow:
5.2 Filesystems
----------------
1. Root (/) should be at least 18MB, and probably no more than 50MB unless
you have some special reason for making your root partition really
large. Remember that the root filesystem is only supposed to contain
vital system files and little else.
Mountpoint Filesystem-size
2. Swap should be at least 2*memory. That is to say if you have 8MB of
memory, then you probably want 16MB of swap. Even more swap space
certainly doesn't hurt, if you can afford to allocate it, and you should
also think ahead a little to any planned memory upgrades you may have
in mind since increasing this later can be very painful!
If you're going to run the X Window System (XFree86), you should also
consider having a *minimum* of 16MB of swap, since X tends to really
use it up.
3. /usr can take up the rest of your disk, though some people like to create
extra partitions for user home directories and the like. Be sure to make
your /usr big enough to contain the system software (about 50MB) and perhaps
some of your own, unless you're going to use symbolic links to point things
like /usr/local (or /usr/src) somewhere else.
Here are some suggested filesystem names and sizes, just for reference:
Mountpoint Filesystem size
-------------------------------
/var 10Mb
/usr 50Mb
@ -191,4 +256,4 @@ Mountpoint Filesystem-size
/usr/X11R6 50Mb If you load the entire XFree86 binary kit.
$Id$
$Id: DISKSPACE.FAQ,v 1.1 1994/11/05 05:54:21 phk Exp $