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authorphk <phk@FreeBSD.org>1994-11-05 05:54:21 +0000
committerphk <phk@FreeBSD.org>1994-11-05 05:54:21 +0000
commitbe6827693224864c9adbfcaa0810e0944309d29c (patch)
treeab8af8f3638eb1921b9a1e5b51ec8e67da3a0fba /share
parentbd82c2541d903286a05d528d9dedb95f8c13a9fc (diff)
downloadFreeBSD-src-be6827693224864c9adbfcaa0810e0944309d29c.zip
FreeBSD-src-be6827693224864c9adbfcaa0810e0944309d29c.tar.gz
This file is the documentation for the fdisk/disklabel part of sysinstall,
and will be available from the boot.flp with just one key-stroke. Somebody will want to purge any danishisms from it before is is let loose...
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+ 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
+---------------------
+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".
+
+1.3 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.
+
+The result is that we have a two-tier structure on the disk:
+
++-----------+
+| MBR-table |
++-----------+ +---------+
+| Slice 1 | -----> | MSDOS |
++-----------+ +---------+
+| Slice 2 |
++-----------+ +-------------------+
+| Slice 3 | -----> | FreeBSD-disklabel |
++-----------+ +-------------------+ +-----------------+
+| Slice 4 | | Partition A | -----> | Root-filesystem |
++-----------+ +-------------------+ +-----------------+
+ | Partition B | ---
+ +-------------------+ \ +----------------+
+ | Partition C | --> | swap-partition |
+ +-------------------+ +----------------+
+ ...
+
+
+Here is the rule-set that FreeBSD uses:
+
+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.
+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.
+
+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)
+ 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
+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.
+
+(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.
+
+(D)isklabel -- enters the Disklabel editor, here you can change how the
+ FreeBSD slice is used.
+
+(Q)uit -- will continue the installation process.
+
+
+3. 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.
+
+Even if you don't plan to have MSDOS on this disk, make a 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.
+
+From the main-screen press 'F' to enter the MBR editor. You have five
+commands available:
+
+(H)elp -- Will launch you into this file.
+
+(D)elete -- Will delete 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.
+
+(R)eread -- This is your "undo" function. It will read the data of the
+ disk again.
+
+(W)rite -- When you are satisfied with the data, this function will write
+ the new MBR to the disk.
+
+(Q)uit -- Go back to the main-screen.
+
+
+4. Disklabel - How to divide the FreeBSD-slice.
+------------------------------------------------
+
+(H)elp -- Will launch you into this file.
+
+(S)ize -- Will resize a partition for you, it will suggest as 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
+ 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.
+
+(D)elete -- Will delete a partition.
+
+(R)eread -- Is a 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.
+
+
+5. Some hints on diskspace needed
+----------------------------------
+
+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.
+
+5.2 Filesystems
+----------------
+
+Mountpoint Filesystem-size
+-------------------------------
+/var 10Mb
+/usr 50Mb
+/ 16Mb
+
+/usr/src 120Mb If you want to have the sources online
+/usr/obj 100Mb If you want to compile all of them at one time
+
+/usr/X11R6 50Mb If you load the entire XFree86 binary kit.
+
+
+$Id$
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