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MULTIBOOTING: SECTION I — PLANNING

October 8, 2008


1. A disk can be divided into four primary partitions or three primary partitions and an extended partition. The extended

partition acts as a container for 16 or so “logical partitions”. Primary/extended partitions are hda1-hda4. Logical partitions are hda5–> (even if not all primary partitions are used). Note that the extended partitions does not have to be last, leading to out-of-order numbering, eg hda1(Prim). hda2(Prim). hda3(Ext)={hda5(Log) hda6(Log)}, hda4(Prim)

2. DOS and pre-XP versions of windows must go on first physical partition.

3. XP can go on logical partitions.

3. XP can use either the NTFS or the FAT file system. NTFS is better on the whole

4. A partition containing shared data in FAT format is a good idea. (Most linuxes have trouble with NTFS). Shared data can reside directly on the XP partition if it is FAT.

5. Some people suggest that windows logical partitions should be placed last (high-numbered) due to a tendency to “wander off”. Alternatively windows logical partitions should not be mixed with linux ones

6. Linuxes are traditionally installed into multiple partitions /boot / /home /usr, etc. This will almost certainly require logical partitions. All linuxes are perfectly happy with logical partitions.

7. Linuxes do not have to be split across multiple partitions — they can be reduced to a single / (root) partition and a swap partition. (having multiple partitions for multiple unixes quickly becomes confusing). The motivation for a traditional multi-partition layout is partly security and stability. If one partition fills up, for instance, other are usuable. This approach should be seriously considered for servers, but is not really necessary for desktop systems. If you have multiple linuxes, or even just a live CD, you can repair a 100% full file system on one linux using another. Putting everything onto one partition is also space-efficient.

8. All swap partitions are exactly the same, and the same swap partition can be used by multiple unixes. Therefore the minimum number of partitions that can be used to install N unixes is N+1. Therefore 16 logical partitions can be used to install 15 linuxes. Therefore a total of 18 OS’s can be installed on a disk, assuming a limit of 16 on logical partitions (not sure about this limit, but I run out of space at this point anyway!). (Swap partitions on disk are used by live disks too!)

9. It is a good idea to give swap partions a low number (eg hda5) so that other linuxes can be re-arranged without changing the “swap” lines in fstab.

10. FreeBSD goes on a primary partition and divides it up by its own technique (like having a second swap partition). It must come *after* the extended partition.

http://www.tldp.org/HOWTO/Linux+FreeBSD-2.html

“This can give you the wrong device assignment and cause the loss of data. My advice is to always put your FreeBSD slice after any Linux extended partitions, and do not change any logical partitions in your Linux extended partitions after installing FreeBSD!”

11. FreeBSD cannot read logical parttiions, therefore shared data should be on a primary partition if BSD is to be used.

12. For maximum flexibility, and disk space allowing, pad out the scheme with unused logical partitions. These can be used to allow the used partitions to stretch and shrink without renumbering. The number of a logical partition is not fixed at creation. If you delete hda6, the old hda7 becomes the new hda6. Renumbering can be compensated for (see section III) but it best avoided. Partitions can be shrunk to something very tiny as an alternative to deleting them (and thus forcing re-numbering).

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