Partitioning your disk simply refers to the act of breaking up your
disk into sections. Each section is then independent of the others.
It’s roughly equivalent to putting up walls in a house; after that,
adding furniture to one room doesn’t affect any other room.
If you already have an operating system on your system (Windows 95,
Windows NT, DOS, etc.) and you want to install Debian GNU/Linux on
the same disk, you will probably need to repartition the disk. In
general, changing a partition that already has a filesystem on it
will destroy any information in that filesystem. Therefore, you
should always make backups before doing any repartitioning. Using
the analogy of the house, you would probably want to move all the
furniture out of the way before moving a wall or you risk destroying
your furniture. Luckily, there is an alternative for some users; see
section 2.3.6 on page [*] for more information.
At a bare minimum, GNU/Linux needs one partition for itself. You can
have a single partition containing the entire operating system,
applications, and your personal files. Most people choose to give
GNU/Linux more than the minimum number of partitions, however. There
are two reasons you might want to break up the filesystem into a
number of smaller partitions. The first is for safety. If something
happens to corrupt the filesystem, generally only one partition is
affected. Thus, you only have to replace (from the backups you’ve
been carefully keeping) a portion of your system. At the very least,
you should consider creating what is commonly called a “root
partition.” This contains the most essential components of the
system. If any other partitions get corrupted, you can still boot
into GNU/Linux to fix the system. This can save you the trouble of
having to reinstall the system from scratch.
The second reason is generally more important in a business setting,
but it really depends on your use of the machine. Suppose something
runs out of control and starts eating disk space. If the process
causing the problem happens to have root privileges (the system
keeps a percentage of the disk away from users), you could suddenly
find yourself out of disk space. This is not good since the
operating system needs to use real files (besides swap space) for
many things. It may not even be a problem of local origin. For
example, unsolicited e-mail (“spam”) can easily fill a partition. By
using more partitions, you protect the system from many of these
problems. Using e-mail as an example again, by putting the directory
/var/spool/mail on its own partition, the bulk of the system will
/work
even if unsolicited e-mail fills that partition.
Another reason applies only if you have a large IDE disk drive and
are using neither LBA addressing nor overlay drivers[5]. In this
case, you will have to put the root partition into the first 1,024
cylinders of your hard drive, usually around 524 megabytes. See
section 2.3.3 on page [*] for more information on this issue.
[5] See your hard drive manual for a description of these features.
Most people feel that a swap partition is also a necessity, although
this isn’t strictly true. “Swap” is scratch space for an operating
system, which allows the system to use disk storage as “virtual
memory” in addition to physical memory. Putting swap on a separate
partition allows Linux to make much more efficient use of it. It is
possible to force Linux to use a regular file as swap, but this is
not recommended.
The only real drawback to using more partitions is that it is often
difficult to know in advance what your needs will be. If you make a
partition too small, either you will have to reinstall the system,
or you will be constantly moving things around to make room in the
undersized partition. On the other hand, if you make the partition
too big, you may be wasting space that could be used elsewhere.