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4. Preparing the Disks


4.a. Introduction to Block Devices

Block Devices

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 SCSI HD in a Linux system, namely /dev/sda.

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.

Partitions and Slices

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 most systems, these are called partitions. Other architectures use a similar technique, called slices.

4.b. Designing a Partitioning Scheme

How Many and How Big?

The number of partitions is highly dependent on your environment. For instance, if you have lots of users, you will most likely want to have your /home separate as it increases security and makes backups easier. If you are installing Gentoo to perform as a mailserver, your /var should be separate as all mails are stored inside /var. A good choice of filesystem will then maximise your performance. Gameservers will have a separate /opt as most gaming servers are installed there. The reason is similar for /home: security and backups. You will definitely want to keep /usr big: not only will it contain the majority of applications, the Portage tree alone takes around 500 Mbyte excluding the various sources that are stored in it.

As you can see, it very much depends on what you want to achieve. Separate partitions or volumes have the following advantages:

  • You can choose the best performing filesystem for each partition or volume
  • Your entire system cannot run out of free space if one defunct tool is continuously writing files to a partition or volume
  • If necessary, file system checks are reduced in time, as multiple checks can be done in parallel (although this advantage is more with multiple disks than it is with multiple partitions)
  • Security can be enhanced by mounting some partitions or volumes read-only, nosuid (setuid bits are ignored), noexec (executable bits are ignored) etc.

However, multiple partitions have one big disadvantage: if not configured properly, you might result in having a system with lots of free space on one partition and none on another. There is also a 15-partition limit for SCSI and SATA.

4.c. Using fdisk on HPPA to Partition your Disk

Use fdisk to create the partitions you want:

Code Listing 3.1: Partitioning the disk

# fdisk /dev/sda

HPPA machines use the PC standard DOS partition tables. To create a new DOS partition table, simply use the o command.

Code Listing 3.2: Creating a DOS partition table

# fdisk /dev/sda

Command (m for help): o
Building a new DOS disklabel.

PALO (the HPPA bootloader) needs a special partition to work. You have to create a partition of at least 16MB at the beginning of your disk. The partition type must be of type f0 (Linux/PA-RISC boot).

Important: If you ignore this and continue without a special PALO partition, your system will stop loving you and fail to start. Also, if your disk is larger than 2GB, make sure that the boot partition is in the first 2GB of your disk. PALO is unable to read a kernel after the 2GB limit.

Code Listing 3.3: A simple default partition schema

# cat /etc/fstab
/dev/sda2    /boot   ext3    noauto,noatime   1 1
/dev/sda3    none    swap    sw               0 0
/dev/sda4    /       ext3    noatime          0 0

# fdisk /dev/sda

Command (m for help): p

Disk /dev/sda: 4294 MB, 4294816768 bytes
133 heads, 62 sectors/track, 1017 cylinders
Units = cylinders of 8246 * 512 = 4221952 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1           8       32953   f0  Linux/PA-RISC boot
/dev/sda2               9          20       49476   83  Linux
/dev/sda3              21          70      206150   82  Linux swap
/dev/sda4              71        1017     3904481   83  Linux

Now that your partitions are created, you can now continue with Creating Filesystems.

4.d. Creating Filesystems


Now that your partitions are created, it is time to place a filesystem on them. If you don't care about what filesystem to choose and are happy with what we use as default in this handbook, continue with Applying a Filesystem to a Partition. Otherwise read on to learn about the available filesystems...


Several filesystems are available. Ext2, ext3, XFS and reiserfs are found stable on the HPPA architecture. The others are very experimental.

ext2 is the tried and true Linux filesystem but doesn't have metadata journaling, which means that routine ext2 filesystem checks at startup time can be quite time-consuming. There is now quite a selection of newer-generation journaled filesystems that can be checked for consistency very quickly and are thus generally preferred over their non-journaled counterparts. Journaled filesystems prevent long delays when you boot your system and your filesystem happens to be in an inconsistent state.

ext3 is the journaled version of the ext2 filesystem, providing metadata journaling for fast recovery in addition to other enhanced journaling modes like full data and ordered data journaling. It uses a hashed B*-tree index that enables high performance in almost all situations. In short, ext3 is a very good and reliable filesystem.

ReiserFS is a B*-tree based filesystem that has very good overall performance and greatly outperforms both ext2 and ext3 when dealing with small files (files less than 4k), often by a factor of 10x-15x. ReiserFS also scales extremely well and has metadata journaling. ReiserFS is solid and usable as both general-purpose filesystem and for extreme cases such as the creation of large filesystems, very large files and directories containing tens of thousands of small files.

XFS is a filesystem with metadata journaling which comes with a robust feature-set and is optimized for scalability. We only recommend using this filesystem on Linux systems with high-end SCSI and/or fibre channel storage and an uninterruptible power supply. Because XFS aggressively caches in-transit data in RAM, improperly designed programs (those that don't take proper precautions when writing files to disk and there are quite a few of them) can lose a good deal of data if the system goes down unexpectedly.

JFS is IBM's high-performance journaling filesystem. It has recently become production-ready and there hasn't been a sufficient track record to comment positively nor negatively on its general stability at this point.

Applying a Filesystem to a Partition

To create a filesystem on a partition or volume, there are tools available for each possible filesystem:

Filesystem Creation Command
ext2 mke2fs
ext3 mke2fs -j
reiserfs mkreiserfs
xfs mkfs.xfs
jfs mkfs.jfs

For instance, to have the boot partition (/dev/sda2 in our example) in ext2 and the root partition (/dev/sda4 in our example) in ext3 (as in our example), you would use:

Code Listing 4.1: Applying a filesystem on a partition

# mke2fs /dev/sda2
# mke2fs -j /dev/sda4

Now create the filesystems on your newly created partitions (or logical volumes).

Activating the Swap Partition

mkswap is the command that is used to initialize swap partitions:

Code Listing 4.2: Creating a Swap signature

# mkswap /dev/sda3

To activate the swap partition, use swapon:

Code Listing 4.3: Activating the swap partition

# swapon /dev/sda3

Create and activate the swap now.

4.e. Mounting

Now that your partitions are initialized and are housing a filesystem, it is time to mount those partitions. Use the mount command. Don't forget to create the necessary mount directories for every partition you created. As an example we mount the root and boot partition:

Code Listing 5.1: Mounting partitions

# mount /dev/sda4 /mnt/gentoo
# mkdir /mnt/gentoo/boot
# mount /dev/sda2 /mnt/gentoo/boot

Note: If you want your /tmp to reside on a separate partition, be sure to change its permissions after mounting: chmod 1777 /mnt/gentoo/tmp. This also holds for /var/tmp.

We will also have to mount the proc filesystem (a virtual interface with the kernel) on /proc. But first we will need to place our files on the partitions.

Continue with Installing the Gentoo Installation Files.

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Page updated November 2, 2006

Summary: To be able to install Gentoo, you must create the necessary partitions. This chapter describes how to partition a disk for future usage.

Sven Vermeulen

Grant Goodyear

Roy Marples

Daniel Robbins

Chris Houser

Jerry Alexandratos

Seemant Kulleen
Gentoo x86 Developer

Tavis Ormandy
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Jason Huebel
Gentoo AMD64 Developer

Guy Martin
Gentoo HPPA developer

Pieter Van den Abeele
Gentoo PPC developer

Joe Kallar
Gentoo SPARC developer

John P. Davis

Pierre-Henri Jondot

Eric Stockbridge

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Jungmin Seo

Stoyan Zhekov

Jared Hudson

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Jorge Paulo

Carl Anderson

Jon Portnoy

Zack Gilburd

Jack Morgan

Benny Chuang


Joshua Kinard

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Gerald J. Normandin Jr.

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Ken Nowack

Lars Weiler

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