Installation guide

80 Appendix D. An Introduction to Disk Partitions
N
The final number denotes the partition. The first four (primary or extended) partitions are num-
bered 1 through 4. Logical partitions start at 5. So, for example, /dev/hda3 is the third primary
or extended partition on the first IDE hard disk, and /dev/sdb6 is the second logical partition
on the second SCSI hard disk.
Note
There is no part of this naming convention that is based on partition type; unlike DOS/Windows, all
partitions can be identified under Red Hat Enterprise Linux. Of course, this does not mean that Red
Hat Enterprise Linux can access data on every type of partition, but in many cases it is possible to
access data on a partition dedicated to another operating system.
Keep this information in mind; it makes things easier to understand when you are setting up the
partitions Red Hat Enterprise Linux requires.
D.1.6. Disk Partitions and Other Operating Systems
If your Red Hat Enterprise Linux partitions are sharing a hard disk with partitions used by other oper-
ating systems, most of the time you will have no problems. However, there are certain combinations
of Linux and other operating systems that require extra care.
D.1.7. Disk Partitions and Mount Points
One area that many people new to Linux find confusing is the matter of how partitions are used and
accessed by the Linux operating system. In DOS/Windows, it is relatively simple: Each partition gets
a "drive letter." You then use the correct drive letter to refer to files and directories on its corresponding
partition.
This is entirely different from how Linux deals with partitions and, for that matter, with disk storage
in general. The main difference is that each partition is used to form part of the storage necessary to
support a single set of files and directories. This is done by associating a partition with a directory
through a process known as mounting. Mounting a partition makes its storage available starting at the
specified directory (known as a mount point).
For example, if partition /dev/hda5 is mounted on /usr/, that would mean that
all files and directories under /usr/ physically reside on /dev/hda5. So the file
/usr/share/doc/FAQ/txt/Linux-FAQ would be stored on /dev/hda5, while the file
/etc/X11/gdm/Sessions/Gnome would not.
Continuing our example, it is also possible that one or more directories below /usr/ would be
mount points for other partitions. For instance, a partition (say, /dev/hda7) could be mounted on
/usr/local/, meaning that /usr/local/man/whatis would then reside on /dev/hda7 rather
than /dev/hda5.
D.1.8. How Many Partitions?
At this point in the process of preparing to install Red Hat Enterprise Linux, you must give some
consideration to the number and size of the partitions to be used by your new operating system. The
question of "how many partitions" continues to spark debate within the Linux community and, without
any end to the debate in sight, it is safe to say that there are probably as many partition layouts as there
are people debating the issue.