en/handbook/hb-install-arm-disk.xml

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<sections>

<version>5.1</version>
<date>2007-06-26</date>

<!-- TODO: Add section about MTD and such -->

<section>
<title>Introduction to Block Devices</title>
<subsection>
<title>Block Devices</title>
<body>

<p>
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.
</p>

<p>
To begin, we'll introduce <e>block devices</e>. The most famous block device is
probably the one that represents the first IDE drive in a Linux system, namely
<path>/dev/hda</path>. If your system uses SCSI or SATA drives, then your 
first hard drive would be <path>/dev/sda</path>.
</p>

<p>
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.
</p>

</body>
</subsection>
<subsection>
<title>Partitions</title>
<body>

<p>
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 <keyval id="arch"/>
systems, these are called <e>partitions</e>. 
</p>

<p>
Partitions are divided in three types:
<e>primary</e>, <e>extended</e> and <e>logical</e>.
</p>

<p>
A <e>primary</e> 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, <path>/dev/hda1</path> to
<path>/dev/hda4</path>).
</p>

<p>
An <e>extended</e> 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.
</p>

<p>
A <e>logical</e> partition is a partition inside the extended partition. Their
definitions aren't placed inside the MBR, but are declared inside the extended
partition. 
</p>

</body>
</subsection>
</section>
<section>
<title>Designing a Partitioning Scheme</title>
<subsection>
<title>Default Partitioning Scheme</title>
<body>

<warn>
The NetWinder firmware, NeTTrom, can only read ext2 partitions realiably so you
must have a separate ext2 boot partition.
</warn>

<p>
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:
</p>

<table>
<tr>
  <th>Partition</th>
  <th>Filesystem</th>
  <th>Size</th>
  <th>Description</th>
</tr>
<tr>
  <ti><path>/dev/hda1</path></ti>
  <ti>ext2</ti>
  <ti>32M</ti>
  <ti>Boot partition</ti>
</tr>
<tr>
  <ti><path>/dev/hda2</path></ti>
  <ti>(swap)</ti>
  <ti>512M</ti>
  <ti>Swap partition</ti>
</tr>
<tr>
  <ti><path>/dev/hda3</path></ti>
  <ti>ext3</ti>
  <ti>Rest of the disk</ti>
  <ti>Root partition</ti>
</tr>
</table>

<p>
If you are interested in knowing how big a partition should be, or even how 
many partitions you need, read on. Otherwise continue now with partitioning 
your disk by reading <uri link="#fdisk">Using fdisk to Partition your
Disk</uri>.
</p>

</body>
</subsection>
<subsection>
<title>How Many and How Big?</title>
<body>

<p>
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
<path>/home</path> separate as it increases security and makes backups easier.
If you are installing Gentoo to perform as a mailserver, your 
<path>/var</path> should be separate as all mails are stored inside 
<path>/var</path>. A good choice of filesystem will then maximise your 
performance. Gameservers will have a separate <path>/opt</path> as most gaming 
servers are installed there. The reason is similar for <path>/home</path>: 
security and backups. You will definitely want to keep <path>/usr</path> 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.
</p>

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

<ul>
<li>
  You can choose the best performing filesystem for each partition or volume
</li>
<li>
  Your entire system cannot run out of free space if one defunct tool is
  continuously writing files to a partition or volume
</li>
<li>
  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)
</li>
<li>
  Security can be enhanced by mounting some partitions or volumes read-only, 
  nosuid (setuid bits are ignored), noexec (executable bits are ignored) etc.
</li>
</ul>

<p>
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.
</p>

<p>
As an example partitioning, we show you one for a 20GB disk, used as a
demonstration laptop (containing webserver, mailserver, gnome, ...):
</p>

<pre caption="Filesystem usage example">
$ <i>df -h</i>
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/hda5     ext3    509M  132M  351M  28% /
/dev/hda2     ext3    5.0G  3.0G  1.8G  63% /home
/dev/hda7     ext3    7.9G  6.2G  1.3G  83% /usr
/dev/hda8     ext3   1011M  483M  477M  51% /opt
/dev/hda9     ext3    2.0G  607M  1.3G  32% /var
/dev/hda1     ext2     51M   17M   31M  36% /boot
/dev/hda6     swap    516M   12M  504M   2% &lt;not mounted&gt;
<comment>(Unpartitioned space for future usage: 2 GB)</comment>
</pre>

<p>
<path>/usr</path> is rather full (83% used) here, but once
all software is installed, <path>/usr</path> doesn't tend to grow that much.
Although allocating a few gigabytes of disk space for <path>/var</path> may
seem excessive, remember that Portage uses this partition by default for
compiling packages. If you want to keep <path>/var</path> at a more reasonable
size, such as 1GB, you will need to alter your <c>PORTAGE_TMPDIR</c> variable
in <path>/etc/make.conf</path> to point to the partition with enough free space
for compiling extremely large packages such as OpenOffice.
</p>

</body>
</subsection>
</section>
<section id="fdisk">
<title>Using fdisk to Partition your Disk</title>
<subsection>
<body>

<p>
The following parts explain how to create the example partition layout 
described previously, namely:
</p>

<table>
<tr>
  <th>Partition</th>
  <th>Description</th>
</tr>
<tr>
  <ti><path>/dev/hda1</path></ti>
  <ti>Boot partition</ti>
</tr>
<tr>
  <ti><path>/dev/hda2</path></ti>
  <ti>Swap partition</ti>
</tr>
<tr>
  <ti><path>/dev/hda3</path></ti>
  <ti>Root partition</ti>
</tr>
</table>

<p>
Change your partition layout according to your own preference.
</p>

</body>
</subsection>
<subsection>
<title>Viewing the Current Partition Layout</title>
<body>

<p>
<c>fdisk</c> is a popular and powerful tool to split your disk into partitions.
Fire up <c>fdisk</c> on your disk (in our example, we use
<path>/dev/hda</path>):
</p>

<pre caption="Starting fdisk">
# <i>fdisk /dev/hda</i>
</pre>

<p>
Once in <c>fdisk</c>, you'll be greeted with a prompt that looks like this:
</p>

<pre caption="fdisk prompt">
Command (m for help): 
</pre>

<p>
Type <c>p</c> to display your disk's current partition configuration:
</p>

<pre caption="An example partition configuration">
Command (m for help): <i>p</i>

Disk /dev/hda: 240 heads, 63 sectors, 2184 cylinders
Units = cylinders of 15120 * 512 bytes

Device Boot    Start       End    Blocks   Id  System
/dev/hda1             1        14    105808+  83  Linux
/dev/hda2            15        49    264600   82  Linux swap
/dev/hda3            50        70    158760   83  Linux
/dev/hda4            71      2184  15981840    5  Extended
/dev/hda5            71       209   1050808+  83  Linux
/dev/hda6           210       348   1050808+  83  Linux
/dev/hda7           349       626   2101648+  83  Linux
/dev/hda8           627       904   2101648+  83  Linux
/dev/hda9           905      2184   9676768+  83  Linux

Command (m for help): 
</pre>

<p>
This particular disk is configured to house seven Linux filesystems (each with
a corresponding partition listed as "Linux") as well as a swap partition
(listed as "Linux swap"). 
</p>

</body>
</subsection>
<subsection>
<title>Removing all Partitions</title>
<body>

<p>
We will first remove all existing partitions from the disk. Type <c>d</c> to
delete a partition. For instance, to delete an existing <path>/dev/hda1</path>:
</p>

<pre caption="Deleting a partition">
Command (m for help): <i>d</i>
Partition number (1-4): <i>1</i>
</pre>

<p>
The partition has been scheduled for deletion. It will no longer show up if you
type <c>p</c>, but it will not be erased until your changes have been saved. If
you made a mistake and want to abort without saving your changes, type <c>q</c>
immediately and hit enter and your partition will not be deleted.
</p>

<p>
Now, assuming that you do indeed want to wipe out all the partitions on your
system, repeatedly type <c>p</c> to print out a partition listing and then type
<c>d</c> and the number of the partition to delete it. Eventually, you'll end 
up with a partition table with nothing in it:
</p>

<pre caption="An empty partition table">
Disk /dev/hda: 30.0 GB, 30005821440 bytes
240 heads, 63 sectors/track, 3876 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes

Device Boot    Start       End    Blocks   Id  System

Command (m for help):
</pre>

<p>
Now that the in-memory partition table is empty, we're ready to create the
partitions. We will use a default partitioning scheme as discussed previously.
Of course, don't follow these instructions to the letter if you don't want the
same partitioning scheme!
</p>

</body>
</subsection>
<subsection>
<title>Creating the Boot Partition</title>
<body>

<p>
We first create a small boot partition. Type <c>n</c> to create a new partition,
then <c>p</c> to select a primary partition, followed by <c>1</c> to select the
first primary partition. When prompted for the first cylinder, hit enter. When
prompted for the last cylinder, type <c>+32M</c> to create a partition 32 Mbyte
in size:
</p>

<pre caption="Creating the boot partition">
Command (m for help): <i>n</i>
Command action
  e   extended
  p   primary partition (1-4)
<i>p</i>
Partition number (1-4): <i>1</i>
First cylinder (1-3876, default 1): <comment>(Hit Enter)</comment>
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-3876, default 3876): <i>+32M</i>
</pre>

<p>
Now, when you type <c>p</c>, you should see the following partition printout:
</p>

<pre caption="Created boot partition">
Command (m for help): <i>p</i>

Disk /dev/hda: 30.0 GB, 30005821440 bytes
240 heads, 63 sectors/track, 3876 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes

Device Boot    Start       End    Blocks   Id  System
/dev/hda1          1        14    105808+  83  Linux
</pre>

<p>
We need to make this partition bootable. Type <c>a</c> to toggle the bootable
flag on a partition and select <c>1</c>. If you press <c>p</c> again, you will 
notice that an <path>*</path> is placed in the "Boot" column.
</p>

</body>
</subsection>
<subsection>
<title>Creating the Swap Partition</title>
<body>

<p>
Let's now create the swap partition. To do this, type <c>n</c> to create a new 
partition, then <c>p</c> to tell fdisk that you want a primary partition. Then 
type <c>2</c> to create the second primary partition, <path>/dev/hda2</path> in
our case. When prompted for the first cylinder, hit enter. When prompted for 
the last cylinder, type <c>+512M</c> to create a partition 512MB in size. After
you've done this, type <c>t</c> to set the partition type, <c>2</c> to select 
the partition you just created and then type in <c>82</c> to set the partition 
type to "Linux Swap". After completing these steps, typing <c>p</c> should
display a partition table that looks similar to this:
</p>

<pre caption="Partition listing after creating a swap partition">
Command (m for help): <i>p</i>

Disk /dev/hda: 30.0 GB, 30005821440 bytes
240 heads, 63 sectors/track, 3876 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes

Device Boot    Start       End    Blocks   Id  System
/dev/hda1 *        1        14    105808+  83  Linux
/dev/hda2         15        81    506520   82  Linux swap
</pre>

</body>
</subsection>
<subsection>
<title>Creating the Root Partition</title>
<body>

<p>
Finally, let's create the root partition. To do this, type <c>n</c> to create a 
new partition, then <c>p</c> to tell fdisk that you want a primary partition. 
Then type <c>3</c> to create the third primary partition, <path>/dev/hda3</path>
in our case. When prompted for the first cylinder, hit enter. When prompted for
the last cylinder, hit enter to create a partition that takes up the rest of the
remaining space on your disk. After completing these steps, typing <c>p</c> 
should display a partition table that looks similar to this:
</p>

<pre caption="Partition listing after creating the root partition">
Command (m for help): <i>p</i>

Disk /dev/hda: 30.0 GB, 30005821440 bytes
240 heads, 63 sectors/track, 3876 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes

Device Boot    Start       End    Blocks   Id  System
/dev/hda1 *        1        14    105808+  83  Linux
/dev/hda2         15        81    506520   82  Linux swap
/dev/hda3         82      3876  28690200   83  Linux
</pre>

</body>
</subsection>
<subsection>
<title>Saving the Partition Layout</title>
<body>

<p>
To save the partition layout and exit <c>fdisk</c>, type <c>w</c>.
</p>

<pre caption="Save and exit fdisk">
Command (m for help): <i>w</i>
</pre>

<p>
Now that your partitions are created, you can now continue with <uri
link="#filesystems">Creating Filesystems</uri>.
</p>

</body>
</subsection>
</section>
<section id="filesystems">
<title>Creating Filesystems</title>
<subsection>
<title>Introduction</title>
<body>

<p>
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 <uri 
link="#filesystems-apply">Applying a Filesystem to a Partition</uri>.
Otherwise read on to learn about the available filesystems...
</p>

</body>
</subsection>
<subsection>
<title>Filesystems?</title>
<body>

<p>
Several filesystems are available. Some of them are found stable on the arm
architecture, others aren't. The following filesystems are found to be stable:
ext2 and ext3. jfs and reiserfs may work but need more testing. If you're
really adventurous you can try the unsupported filesystems.
</p>

<p>
<b>ext2</b> 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.
</p>

<p>
<b>ext3</b> 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 an HTree index that enables high
performance in almost all situations. In short, ext3 is a very good and reliable
filesystem.
</p>

<p>
<b>ReiserFS</b> 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.
</p>

<p>
<b>XFS</b> 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.
</p>

<p>
<b>JFS</b> 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.
</p>

</body>
</subsection>
<subsection id="filesystems-apply">
<title>Applying a Filesystem to a Partition</title>
<body>

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

<table>
<tr>
  <th>Filesystem</th>
  <th>Creation Command</th>
</tr>
<tr>
  <ti>ext2</ti>
  <ti><c>mke2fs</c></ti>
</tr>
<tr>
  <ti>ext3</ti>
  <ti><c>mke2fs -j</c></ti>
</tr>
<tr>
  <ti>reiserfs</ti>
  <ti><c>mkreiserfs</c></ti>
</tr>
<tr>
  <ti>xfs</ti>
  <ti><c>mkfs.xfs</c></ti>
</tr>
<tr>
  <ti>jfs</ti>
  <ti><c>mkfs.jfs</c></ti>
</tr>
</table>

<p>
For instance, to have the boot partition (<path>/dev/hda1</path> in our
example) in ext2 and the root partition (<path>/dev/hda3</path> in our example)
in ext3 (as in our example), you would use:
</p>

<pre caption="Applying a filesystem on a partition">
# <i>mke2fs /dev/hda1</i>
# <i>mke2fs -j /dev/hda3</i>
</pre>

<p>
Now create the filesystems on your newly created partitions (or logical
volumes).
</p>

</body>
</subsection>
<subsection>
<title>Activating the Swap Partition</title>
<body>

<p>
<c>mkswap</c> is the command that is used to initialize swap partitions:
</p>

<pre caption="Creating a Swap signature">
# <i>mkswap /dev/hda2</i>
</pre>

<p>
To activate the swap partition, use <c>swapon</c>:
</p>

<pre caption="Activating the swap partition">
# <i>swapon /dev/hda2</i>
</pre>

<p>
Create and activate the swap with the commands mentioned above.
</p>

</body>
</subsection>
</section>
<section>
<title>Mounting</title>
<body>

<p>
Now that your partitions are initialized and are housing a filesystem, it is
time to mount those partitions. Use the <c>mount</c> 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:
</p>

<pre caption="Mounting partitions">
# <i>mount /dev/hda3 /mnt/gentoo</i>
# <i>mkdir /mnt/gentoo/boot</i>
# <i>mount /dev/hda1 /mnt/gentoo/boot</i>
</pre>

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

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

<p>
Continue with <uri link="?part=1&amp;chap=5">Installing the Gentoo
Installation Files</uri>.
</p>

</body>
</section>
</sections>