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4. Preparing the Disks
4.a. Introduction to 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
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,
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).
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. ext3 is a very good and reliable
filesystem. It has an additional hashed b-tree indexing option that enables
high performance in almost all situations. You can enable this indexing by
adding -O dir_index to the mke2fs command. In short, ext3 is an
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. As of kernel 2.4.18+, ReiserFS is
solid and usable as both general-purpose filesystem and for extreme cases such
as the creation of large filesystems, the use of many small files, very large
files and directories containing tens of thousands of 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:
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
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.
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
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
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