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diff --git a/share/FAQ/diskspace.FAQ b/share/FAQ/diskspace.FAQ new file mode 100644 index 0000000..ce7c29c --- /dev/null +++ b/share/FAQ/diskspace.FAQ @@ -0,0 +1,265 @@ + How to assign disk space to FreeBSD. + +1.0 Getting started. +--------------------- + +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 (or may not) enjoy the brief history lesson. + + +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 manageable 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 "slices". What it had was a way to install +Xenix and MS-DOS on the same disk (Remember when Microsoft were in the UNIX +business?). + +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. They also reserved +only 10 bits for cylinder addressing, limiting DOS to being able to address +a maximum of 1024 cylinders (and cause of the dreaded "cylinder translation" +kludges, the misconfiguration of which many users have seen as the notorious +"Missing Operating System" message). 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-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: + ++-----------+ +| MBR-table | ++-----------+ +---------+ +| Slice 1 | -----> | MSDOS | ++-----------+ +---------+ +| Slice 2 | ++-----------+ +-------------------+ +| Slice 3 | -----> | FreeBSD-disklabel | ++-----------+ +-------------------+ +-----------------+ +| Slice 4 | | Partition A | -----> | Root-filesystem | ++-----------+ +-------------------+ +-----------------+ + | Partition B | --- + +-------------------+ \ +----------------+ + | Partition C | --> | swap-partition | + +-------------------+ +----------------+ + | ... | + + +Here are the rules that FreeBSD plays by: + +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 secondary 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 an 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: + + Step FreeBSD utility + ------------------------------------------------------------ --------------- + 1. Make an MBR slice for FreeBSD (FDISK) + 2. Partition the diskspace in the MBR slice into partitions (DISKLABEL) + 3. Assign mountpoints to the partitions. (DISKLABEL) + + + +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 (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. + +(D)isklabel -- enters the Disklabel editor, here you can change how the + FreeBSD slice is partitioned for FreeBSD. + +(P)rocede -- will continue the installation process. + +(Q)uit -- Go back to the entry screen. + + +2.2 FDISK - how to make an MBR slice +------------------------------------- +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 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 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 +commands available: + +(H)elp -- Shows you this file. + +(D)elete -- Deletes a slice entirely. + +(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, 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. + +(Q)uit -- Go back to the main screen. + + +2.3 Disklabel - How to divide up the FreeBSD slice. +---------------------------------------------------- + +The disklabel screen provides the following commands: + +(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 + and may say zero, even though there is diskspace available. If it + does, delete and resize the other partitions. + +(A)ssign -- Here you assign where the filesystem in a partition is to + be mounted. `b' partitions will always be made into "swap" partitions. + +(D)elete -- Delete a partition. + +(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. + + +2.4. Hints on partition sizing +------------------------------- + +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: + +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. + +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 +/ 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: DISKSPACE.FAQ,v 1.7 1994/11/21 01:30:03 jkh Exp $ |
