Gentoo Linux AMD64 Handbook

Chapter 4. Preparing the Disks
Introduction to Block Devices
Block Devices
Partitions
We'll take a good look at disk-oriented aspects of Gentoo Linux and Linux in general, including Linux
filesystems, partitions and block devices. Then, once you're familiar with the ins and outs of disks
and filesystems, you'll be guided through the process of setting up partitions and filesystems for your
Gentoo Linux installation.
To begin, we'll introduce block devices. The most famous block device is probably the one that
represents the first drive in a Linux system, namely /dev/sda. SCSI and Serial ATA drives are both
labeled /dev/sd*; even IDE drives are labeled /dev/sd* with the new libata framework in the
kernel. If you're using the old device framework, then your first IDE drive is /dev/hda.
The block devices above represent an abstract interface to the disk. User programs can use these
block devices to interact with your disk without worrying about whether your drives are IDE, SCSI
or something else. The program can simply address the storage on the disk as a bunch of contiguous,
randomly-accessible 512-byte blocks.
Although it is theoretically possible to use a full disk to house your Linux system, this is almost
never done in practice. Instead, full disk block devices are split up in smaller, more manageable block
devices. On AMD64 systems, these are called partitions.
Partitions are divided in three types: primary, extended and logical.
A primary partition is a partition which has its information stored in the MBR (master boot record).
As an MBR is very small (512 bytes) only four primary partitions can be defined (for instance, /dev/
sda1 to /dev/sda4).
An extended partition is a special primary partition (meaning the extended partition must be one
of the four possible primary partitions) which contains more partitions. Such a partition didn't exist
originally, but as four partitions were too few, it was brought to life to extend the formatting scheme
without losing backward compatibility.
A logical partition is a partition inside the extended partition. Their definitions aren't placed inside the
MBR, but are declared inside the extended partition.
Advanced Storage
The AMD64 Installation CDs provide support for LVM2. LVM2 increases the flexibility offered by
your partitioning setup. During the installation instructions, we will focus on "regular" partitions, but
it is still good to know LVM2 is supported as well.
Designing a Partitioning Scheme
Default Partitioning Scheme
If you are not interested in drawing up a partitioning scheme for your system, you can use the
partitioning scheme we use throughout this book:
Partition Filesystem Size Description
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